diff --git a/applications/utilities/parallelProcessing/redistributePar/redistributePar.C b/applications/utilities/parallelProcessing/redistributePar/redistributePar.C
index 45dd9210c9..e81ca5ef3d 100644
--- a/applications/utilities/parallelProcessing/redistributePar/redistributePar.C
+++ b/applications/utilities/parallelProcessing/redistributePar/redistributePar.C
@@ -511,9 +511,9 @@ void writeProcAddressing
             patchDistMap.constructMap(),
             patchDistMap.constructHasFlip(),
             patchMap,
+            label(-1),
             eqOp<label>(),
             flipOp(),
-            label(-1),
             UPstream::msgType()
         );
     }
diff --git a/src/OpenFOAM/db/IOstreams/Pstreams/UPstream.C b/src/OpenFOAM/db/IOstreams/Pstreams/UPstream.C
index 51a1dfaf94..3b65d8a199 100644
--- a/src/OpenFOAM/db/IOstreams/Pstreams/UPstream.C
+++ b/src/OpenFOAM/db/IOstreams/Pstreams/UPstream.C
@@ -90,8 +90,8 @@ void Foam::UPstream::setParRun(const label nProcs, const bool haveThreads)
                 << Foam::exit(FatalError);
         }
 
-        Pout.prefix() = '[' +  name(myProcNo(Pstream::worldComm)) + "] ";
-        Perr.prefix() = '[' +  name(myProcNo(Pstream::worldComm)) + "] ";
+        Pout.prefix() = '[' +  name(myProcNo(comm)) + "] ";
+        Perr.prefix() = '[' +  name(myProcNo(comm)) + "] ";
     }
 }
 
@@ -373,6 +373,8 @@ Foam::DynamicList<Foam::List<int>> Foam::UPstream::procIDs_(10);
 
 Foam::DynamicList<Foam::label> Foam::UPstream::parentCommunicator_(10);
 
+Foam::wordList Foam::UPstream::allWorlds_(1, "");
+Foam::labelList Foam::UPstream::worldIDs_(1, 0);
 
 Foam::DynamicList<Foam::List<Foam::UPstream::commsStruct>>
 Foam::UPstream::linearCommunication_(10);
diff --git a/src/OpenFOAM/db/IOstreams/Pstreams/UPstream.H b/src/OpenFOAM/db/IOstreams/Pstreams/UPstream.H
index c0f3d40d5c..32042e4cbc 100644
--- a/src/OpenFOAM/db/IOstreams/Pstreams/UPstream.H
+++ b/src/OpenFOAM/db/IOstreams/Pstreams/UPstream.H
@@ -194,6 +194,13 @@ private:
         //- Standard transfer message type
         static int msgType_;
 
+        //- Names of all worlds
+        static wordList allWorlds_;
+
+        //- Per processor the name of the world
+        static labelList worldIDs_;
+
+
         // Communicator specific data
 
         //- Free communicators
@@ -437,7 +444,7 @@ public:
         }
 
         //- Number of processes in parallel run, and 1 for serial run
-        static label nProcs(const label communicator = 0)
+        static label nProcs(const label communicator = worldComm)
         {
             return procIDs_[communicator].size();
         }
@@ -449,13 +456,13 @@ public:
         }
 
         //- Am I the master process
-        static bool master(const label communicator = 0)
+        static bool master(const label communicator = worldComm)
         {
             return myProcNo_[communicator] == masterNo();
         }
 
         //- Number of this process (starting from masterNo() = 0)
-        static int myProcNo(const label communicator = 0)
+        static int myProcNo(const label communicator = worldComm)
         {
             return myProcNo_[communicator];
         }
@@ -471,15 +478,43 @@ public:
             return procIDs_[communicator];
         }
 
+
+        // Worlds
+
+            //- All worlds
+            static const wordList& allWorlds()
+            {
+                return allWorlds_;
+            }
+
+            //- worldID (index in allWorlds) of all processes
+            static const labelList& worldIDs()
+            {
+                return worldIDs_;
+            }
+
+            //- My worldID
+            static label myWorldID()
+            {
+                return worldIDs_[myProcNo(0)];
+            }
+
+            //- My world
+            static const word& myWorld()
+            {
+                return allWorlds()[myWorldID()];
+            }
+
+
         //- Range of process indices for all processes
-        static rangeType allProcs(const label communicator = 0)
+        static rangeType allProcs(const label communicator = worldComm)
         {
             // Proc 0 -> nProcs (int value)
             return rangeType(static_cast<int>(nProcs(communicator)));
         }
 
         //- Range of process indices for sub-processes
-        static rangeType subProcs(const label communicator = 0)
+        static rangeType subProcs(const label communicator = worldComm)
         {
             // Proc 1 -> nProcs (int value)
             return rangeType(1, static_cast<int>(nProcs(communicator)-1));
@@ -488,7 +523,7 @@ public:
         //- Communication schedule for linear all-to-master (proc 0)
         static const List<commsStruct>& linearCommunication
         (
-            const label communicator = 0
+            const label communicator = worldComm
         )
         {
             return linearCommunication_[communicator];
@@ -497,7 +532,7 @@ public:
         //- Communication schedule for tree all-to-master (proc 0)
         static const List<commsStruct>& treeCommunication
         (
-            const label communicator = 0
+            const label communicator = worldComm
         )
         {
             return treeCommunication_[communicator];
@@ -542,7 +577,7 @@ public:
         (
             const labelUList& sendData,
             labelUList& recvData,
-            const label communicator = 0
+            const label communicator = worldComm
         );
 
         //- Exchange data with all processors (in the communicator)
@@ -559,7 +594,7 @@ public:
             const UList<int>& recvSizes,
             const UList<int>& recvOffsets,
 
-            const label communicator = 0
+            const label communicator = worldComm
         );
 
         //- Receive data from all processors on the master
@@ -571,7 +606,7 @@ public:
             char* recvData,
             const UList<int>& recvSizes,
             const UList<int>& recvOffsets,
-            const label communicator = 0
+            const label communicator = worldComm
         );
 
         //- Send data to all processors from the root of the communicator
@@ -583,7 +618,7 @@ public:
 
             char* recvData,
             int recvSize,
-            const label communicator = 0
+            const label communicator = worldComm
         );
 
 
@@ -598,7 +633,7 @@ public:
 
         //- Process index of last sub-process
         //  \deprecated(2020-09) use subProcs() method instead
-        static int lastSlave(const label communicator = 0)
+        static int lastSlave(const label communicator = worldComm)
         {
             return nProcs(communicator) - 1;
         }
diff --git a/src/OpenFOAM/global/argList/argList.C b/src/OpenFOAM/global/argList/argList.C
index 2e1d2fc48d..615d395f9f 100644
--- a/src/OpenFOAM/global/argList/argList.C
+++ b/src/OpenFOAM/global/argList/argList.C
@@ -166,6 +166,20 @@ Foam::argList::initValidTables::initValidTables()
         true  // advanced option
     );
 
+    argList::addOption
+    (
+        "world",
+        "Name",
+        "Name of local world",
+        true
+    );
+    validParOptions.set
+    (
+        "world",
+        "Name of local world"
+    );
+
+
     // Some standard option aliases (with or without version warnings)
 //     argList::addOptionCompat
 //     (
@@ -493,6 +507,7 @@ void Foam::argList::noParallel()
     removeOption("roots");
     removeOption("decomposeParDict");
     removeOption("hostRoots");
+    removeOption("world");
     validParOptions.clear();
 }
 
@@ -711,6 +726,7 @@ void Foam::argList::setCasePaths()
         }
         else
         {
+            caseDir.expand();
             caseDir.toAbsolute();
         }
     }
@@ -1241,7 +1257,7 @@ void Foam::argList::parse
                     dictNProcs = roots.size()+1;
                 }
             }
-            else if (checkProcessorDirectories_)
+            else if (checkProcessorDirectories_ && Pstream::nProcs() > 1)
             {
                 // Use values from decomposeParDict, the location was already
                 // established above.
@@ -1268,6 +1284,13 @@ void Foam::argList::parse
                 Pstream::parRun(oldParRun);  // Restore parallel state
 
                 decompDict.readEntry("numberOfSubdomains", dictNProcs);
+                if (Pstream::nProcs() == 1)
+                {
+                    WarningInFunction
+                        << "Running parallel on single processor. This only"
+                        << " makes sense for multi-world simulation" << endl;
+                    dictNProcs = 1;
+                }
 
                 if (decompDict.getOrDefault("distributed", false))
                 {
@@ -1300,7 +1323,12 @@ void Foam::argList::parse
             // - normal running : nProcs = dictNProcs = nProcDirs
             // - decomposition to more  processors : nProcs = dictNProcs
             // - decomposition to fewer processors : nProcs = nProcDirs
-            if (checkProcessorDirectories_ && dictNProcs > Pstream::nProcs())
+            if
+            (
+                checkProcessorDirectories_
+             && Pstream::nProcs() > 1
+             && dictNProcs > Pstream::nProcs()
+            )
             {
                 FatalError
                     << source
@@ -1353,6 +1381,7 @@ void Foam::argList::parse
                 if
                 (
                     checkProcessorDirectories_
+                 && Pstream::nProcs() > 1
                  && dictNProcs < Pstream::nProcs()
                 )
                 {
@@ -1405,7 +1434,14 @@ void Foam::argList::parse
         }
 
         nProcs = Pstream::nProcs();
-        case_ = globalCase_/("processor" + Foam::name(Pstream::myProcNo()));
+        if (Pstream::nProcs() > 1)
+        {
+            case_ = globalCase_/("processor" + Foam::name(Pstream::myProcNo()));
+        }
+        else
+        {
+            case_ = globalCase_;
+        }
     }
     else
     {
@@ -1468,6 +1504,13 @@ void Foam::argList::parse
                 << Pstream::commsTypeNames[Pstream::defaultCommsType] << nl
                 << "    polling iterations : " << Pstream::nPollProcInterfaces
                 << endl;
+            if (UPstream::allWorlds().size() > 1)
+            {
+                Info<< "    worlds             : "
+                    << flatOutput(UPstream::allWorlds()) << nl
+                    << "    world              : " << UPstream::myWorld()
+                    << endl;
+            }
         }
     }
 
diff --git a/src/OpenFOAM/meshes/polyMesh/globalMeshData/globalIndexI.H b/src/OpenFOAM/meshes/polyMesh/globalMeshData/globalIndexI.H
index 452f034b32..04e51697b0 100644
--- a/src/OpenFOAM/meshes/polyMesh/globalMeshData/globalIndexI.H
+++ b/src/OpenFOAM/meshes/polyMesh/globalMeshData/globalIndexI.H
@@ -93,7 +93,7 @@ inline Foam::label Foam::globalIndex::size() const
 
 inline void Foam::globalIndex::reset(const label localSize)
 {
-    reset(localSize, Pstream::msgType(), 0, true);
+    reset(localSize, Pstream::msgType(), UPstream::worldComm, true);
 }
 
 
diff --git a/src/OpenFOAM/meshes/polyMesh/globalMeshData/globalMeshData.C b/src/OpenFOAM/meshes/polyMesh/globalMeshData/globalMeshData.C
index c553ca8aff..b3f7aed676 100644
--- a/src/OpenFOAM/meshes/polyMesh/globalMeshData/globalMeshData.C
+++ b/src/OpenFOAM/meshes/polyMesh/globalMeshData/globalMeshData.C
@@ -2745,13 +2745,16 @@ void Foam::globalMeshData::updateMesh()
 
     // *** Temporary hack to avoid problems with overlapping communication
     // *** between these reductions and the calculation of deltaCoeffs
-    //label comm = UPstream::worldComm + 1;
-    label comm = UPstream::allocateCommunicator
+    //const label comm = UPstream::worldComm + 1;
+    const label comm = UPstream::allocateCommunicator
     (
         UPstream::worldComm,
         identity(UPstream::nProcs(UPstream::worldComm)),
         true
     );
+    const label oldWarnComm = UPstream::warnComm;
+    UPstream::warnComm = comm;
+
 
     // Total number of faces.
     nTotalFaces_ = returnReduce
@@ -2789,6 +2792,7 @@ void Foam::globalMeshData::updateMesh()
     );
 
     UPstream::freeCommunicator(comm);
+    UPstream::warnComm = oldWarnComm;
 
     if (debug)
     {
diff --git a/src/OpenFOAM/meshes/polyMesh/mapPolyMesh/mapDistribute/mapDistribute.C b/src/OpenFOAM/meshes/polyMesh/mapPolyMesh/mapDistribute/mapDistribute.C
index 5551bcc0b4..d90582e894 100644
--- a/src/OpenFOAM/meshes/polyMesh/mapPolyMesh/mapDistribute/mapDistribute.C
+++ b/src/OpenFOAM/meshes/polyMesh/mapPolyMesh/mapDistribute/mapDistribute.C
@@ -148,9 +148,9 @@ void Foam::mapDistribute::printLayout(Ostream& os) const
 
 // * * * * * * * * * * * * * * * * Constructors  * * * * * * * * * * * * * * //
 
-Foam::mapDistribute::mapDistribute()
+Foam::mapDistribute::mapDistribute(const label comm)
 :
-    mapDistributeBase()
+    mapDistributeBase(comm)
 {}
 
 
@@ -176,7 +176,8 @@ Foam::mapDistribute::mapDistribute
     labelListList&& subMap,
     labelListList&& constructMap,
     const bool subHasFlip,
-    const bool constructHasFlip
+    const bool constructHasFlip,
+    const label comm
 )
 :
     mapDistributeBase
@@ -185,7 +186,8 @@ Foam::mapDistribute::mapDistribute
         std::move(subMap),
         std::move(constructMap),
         subHasFlip,
-        constructHasFlip
+        constructHasFlip,
+        comm
     )
 {}
 
@@ -198,7 +200,8 @@ Foam::mapDistribute::mapDistribute
     labelListList&& transformElements,
     labelList&& transformStart,
     const bool subHasFlip,
-    const bool constructHasFlip
+    const bool constructHasFlip,
+    const label comm
 )
 :
     mapDistributeBase
@@ -207,7 +210,8 @@ Foam::mapDistribute::mapDistribute
         std::move(subMap),
         std::move(constructMap),
         subHasFlip,
-        constructHasFlip
+        constructHasFlip,
+        comm
     ),
     transformElements_(std::move(transformElements)),
     transformStart_(std::move(transformStart))
@@ -217,10 +221,11 @@ Foam::mapDistribute::mapDistribute
 Foam::mapDistribute::mapDistribute
 (
     const labelUList& sendProcs,
-    const labelUList& recvProcs
+    const labelUList& recvProcs,
+    const label comm
 )
 :
-    mapDistributeBase(sendProcs, recvProcs)
+    mapDistributeBase(sendProcs, recvProcs, comm)
 {}
 
 
@@ -229,7 +234,8 @@ Foam::mapDistribute::mapDistribute
     const globalIndex& globalNumbering,
     labelList& elements,
     List<Map<label>>& compactMap,
-    const int tag
+    const int tag,
+    const label comm
 )
 :
     mapDistributeBase
@@ -237,7 +243,8 @@ Foam::mapDistribute::mapDistribute
         globalNumbering,
         elements,
         compactMap,
-        tag
+        tag,
+        comm
     )
 {}
 
@@ -247,7 +254,8 @@ Foam::mapDistribute::mapDistribute
     const globalIndex& globalNumbering,
     labelListList& cellCells,
     List<Map<label>>& compactMap,
-    const int tag
+    const int tag,
+    const label comm
 )
 :
     mapDistributeBase
@@ -255,7 +263,8 @@ Foam::mapDistribute::mapDistribute
         globalNumbering,
         cellCells,
         compactMap,
-        tag
+        tag,
+        comm
     )
 {}
 
@@ -268,11 +277,14 @@ Foam::mapDistribute::mapDistribute
     const labelPairList& transformedElements,
     labelList& transformedIndices,
     List<Map<label>>& compactMap,
-    const int tag
+    const int tag,
+    const label comm
 )
 :
-    mapDistributeBase()
+    mapDistributeBase(comm)
 {
+    const label myRank = Pstream::myProcNo(comm);
+
     // Construct per processor compact addressing of the global elements
     // needed. The ones from the local processor are not included since
     // these are always all needed.
@@ -288,7 +300,7 @@ Foam::mapDistribute::mapDistribute
     {
         labelPair elem = transformedElements[i];
         label proci = globalTransforms.processor(elem);
-        if (proci != Pstream::myProcNo())
+        if (proci != myRank)
         {
             label index = globalTransforms.index(elem);
             label nCompact = compactMap[proci].size();
@@ -345,7 +357,7 @@ Foam::mapDistribute::mapDistribute
         // Get compact index for untransformed element
         label rawElemI =
         (
-            proci == Pstream::myProcNo()
+            proci == myRank
           ? index
           : compactMap[proci][index]
         );
@@ -373,11 +385,14 @@ Foam::mapDistribute::mapDistribute
     const List<labelPairList>& transformedElements,
     labelListList& transformedIndices,
     List<Map<label>>& compactMap,
-    const int tag
+    const int tag,
+    const label comm
 )
 :
-    mapDistributeBase()
+    mapDistributeBase(comm)
 {
+    const label myRank = Pstream::myProcNo(comm_);
+
     // Construct per processor compact addressing of the global elements
     // needed. The ones from the local processor are not included since
     // these are always all needed.
@@ -396,7 +411,7 @@ Foam::mapDistribute::mapDistribute
         forAll(elems, i)
         {
             label proci = globalTransforms.processor(elems[i]);
-            if (proci != Pstream::myProcNo())
+            if (proci != myRank)
             {
                 label index = globalTransforms.index(elems[i]);
                 label nCompact = compactMap[proci].size();
@@ -462,7 +477,7 @@ Foam::mapDistribute::mapDistribute
             // Get compact index for untransformed element
             label rawElemI =
             (
-                proci == Pstream::myProcNo()
+                proci == myRank
               ? index
               : compactMap[proci][index]
             );
@@ -487,10 +502,11 @@ Foam::mapDistribute::mapDistribute
 (
     labelListList&& subMap,
     const bool subHasFlip,
-    const bool constructHasFlip
+    const bool constructHasFlip,
+    const label comm
 )
 :
-    mapDistributeBase(std::move(subMap), subHasFlip, constructHasFlip)
+    mapDistributeBase(std::move(subMap), subHasFlip, constructHasFlip, comm)
 {}
 
 
diff --git a/src/OpenFOAM/meshes/polyMesh/mapPolyMesh/mapDistribute/mapDistribute.H b/src/OpenFOAM/meshes/polyMesh/mapPolyMesh/mapDistribute/mapDistribute.H
index 5b4a812bb4..ddeba70662 100644
--- a/src/OpenFOAM/meshes/polyMesh/mapPolyMesh/mapDistribute/mapDistribute.H
+++ b/src/OpenFOAM/meshes/polyMesh/mapPolyMesh/mapDistribute/mapDistribute.H
@@ -328,7 +328,7 @@ public:
     // Constructors
 
         //- Construct null
-        mapDistribute();
+        mapDistribute(const label comm = UPstream::worldComm);
 
         //- Copy construct
         explicit mapDistribute(const mapDistribute& map);
@@ -343,7 +343,8 @@ public:
             labelListList&& subMap,
             labelListList&& constructMap,
             const bool subHasFlip = false,
-            const bool constructHasFlip = false
+            const bool constructHasFlip = false,
+            const label comm = UPstream::worldComm
         );
 
         //- Move construct from components
@@ -355,7 +356,8 @@ public:
             labelListList&& transformElements,
             labelList&& transformStart,
             const bool subHasFlip = false,
-            const bool constructHasFlip = false
+            const bool constructHasFlip = false,
+            const label comm = UPstream::worldComm
         );
 
         //- Construct from reverse addressing: per data item the send
@@ -365,7 +367,8 @@ public:
         mapDistribute
         (
             const labelUList& sendProcs,
-            const labelUList& recvProcs
+            const labelUList& recvProcs,
+            const label comm = UPstream::worldComm
         );
 
         //- Construct from list of (possibly) remote elements in globalIndex
@@ -378,7 +381,8 @@ public:
             const globalIndex&,
             labelList& elements,
             List<Map<label>>& compactMap,
-            const int tag = Pstream::msgType()
+            const int tag = Pstream::msgType(),
+            const label comm = UPstream::worldComm
         );
 
         //- Special variant that works with the info sorted into bins
@@ -390,7 +394,8 @@ public:
             const globalIndex&,
             labelListList& cellCells,
             List<Map<label>>& compactMap,
-            const int tag = Pstream::msgType()
+            const int tag = Pstream::msgType(),
+            const label comm = UPstream::worldComm
         );
 
         //- Construct from list of (possibly remote) untransformed elements
@@ -407,7 +412,8 @@ public:
             const labelPairList& transformedElements,
             labelList& transformedIndices,
             List<Map<label>>& compactMap,
-            const int tag = Pstream::msgType()
+            const int tag = Pstream::msgType(),
+            const label comm = UPstream::worldComm
         );
 
         //- As above but with ListLists.
@@ -419,7 +425,8 @@ public:
             const List<labelPairList>& transformedElements,
             labelListList& transformedIndices,
             List<Map<label>>& compactMap,
-            const int tag = Pstream::msgType()
+            const int tag = Pstream::msgType(),
+            const label comm = UPstream::worldComm
         );
 
         //- Construct from my elements to send. Assumes layout is my elements
@@ -429,7 +436,8 @@ public:
         (
             labelListList&& subMap,
             const bool subHasFlip = false,
-            const bool constructHasFlip = false
+            const bool constructHasFlip = false,
+            const label comm = UPstream::worldComm
         );
 
         //- Construct from Istream
diff --git a/src/OpenFOAM/meshes/polyMesh/mapPolyMesh/mapDistribute/mapDistributeBase.C b/src/OpenFOAM/meshes/polyMesh/mapPolyMesh/mapDistribute/mapDistributeBase.C
index 59c0095099..eabb926220 100644
--- a/src/OpenFOAM/meshes/polyMesh/mapPolyMesh/mapDistribute/mapDistributeBase.C
+++ b/src/OpenFOAM/meshes/polyMesh/mapPolyMesh/mapDistribute/mapDistributeBase.C
@@ -46,29 +46,33 @@ Foam::List<Foam::labelPair> Foam::mapDistributeBase::schedule
 (
     const labelListList& subMap,
     const labelListList& constructMap,
-    const int tag
+    const int tag,
+    const label comm
 )
 {
+    const label myRank = Pstream::myProcNo(comm);
+    const label nProcs = Pstream::nProcs(comm);
+
     // Communications: send and receive processor
     List<labelPair> allComms;
 
     {
-        labelPairHashSet commsSet(Pstream::nProcs());
+        labelPairHashSet commsSet(nProcs);
 
         // Find what communication is required
         forAll(subMap, proci)
         {
-            if (proci != Pstream::myProcNo())
+            if (proci != myRank)
             {
                 if (subMap[proci].size())
                 {
                     // I need to send to proci
-                    commsSet.insert(labelPair(Pstream::myProcNo(), proci));
+                    commsSet.insert(labelPair(myRank, proci));
                 }
                 if (constructMap[proci].size())
                 {
                     // I need to receive from proci
-                    commsSet.insert(labelPair(proci, Pstream::myProcNo()));
+                    commsSet.insert(labelPair(proci, myRank));
                 }
             }
         }
@@ -77,12 +81,19 @@ Foam::List<Foam::labelPair> Foam::mapDistributeBase::schedule
 
 
     // Reduce
-    if (Pstream::master())
+    if (Pstream::master(comm))
     {
         // Receive and merge
-        for (const int slave : Pstream::subProcs())
+        for (const int slave : Pstream::subProcs(comm))
         {
-            IPstream fromSlave(Pstream::commsTypes::scheduled, slave, 0, tag);
+            IPstream fromSlave
+            (
+                Pstream::commsTypes::scheduled,
+                slave,
+                0,
+                tag,
+                comm
+            );
             List<labelPair> nbrData(fromSlave);
 
             forAll(nbrData, i)
@@ -96,9 +107,16 @@ Foam::List<Foam::labelPair> Foam::mapDistributeBase::schedule
             }
         }
         // Send back
-        for (const int slave : Pstream::subProcs())
+        for (const int slave : Pstream::subProcs(comm))
         {
-            OPstream toSlave(Pstream::commsTypes::scheduled, slave, 0, tag);
+            OPstream toSlave
+            (
+                Pstream::commsTypes::scheduled,
+                slave,
+                0,
+                tag,
+                comm
+            );
             toSlave << allComms;
         }
     }
@@ -110,7 +128,8 @@ Foam::List<Foam::labelPair> Foam::mapDistributeBase::schedule
                 Pstream::commsTypes::scheduled,
                 Pstream::masterNo(),
                 0,
-                tag
+                tag,
+                comm
             );
             toMaster << allComms;
         }
@@ -120,7 +139,8 @@ Foam::List<Foam::labelPair> Foam::mapDistributeBase::schedule
                 Pstream::commsTypes::scheduled,
                 Pstream::masterNo(),
                 0,
-                tag
+                tag,
+                comm
             );
             fromMaster >> allComms;
         }
@@ -132,9 +152,9 @@ Foam::List<Foam::labelPair> Foam::mapDistributeBase::schedule
     (
         commSchedule
         (
-            Pstream::nProcs(),
+            nProcs,
             allComms
-        ).procSchedule()[Pstream::myProcNo()]
+        ).procSchedule()[myRank]
     );
 
     // Processors involved in my schedule
@@ -151,7 +171,7 @@ Foam::List<Foam::labelPair> Foam::mapDistributeBase::schedule
     //        label sendProc = twoProcs[0];
     //        label recvProc = twoProcs[1];
     //
-    //        if (recvProc == Pstream::myProcNo())
+    //        if (recvProc == myRank)
     //        {
     //            Pout<< "    receive from " << sendProc << endl;
     //        }
@@ -172,7 +192,7 @@ const Foam::List<Foam::labelPair>& Foam::mapDistributeBase::schedule() const
         (
             new List<labelPair>
             (
-                schedule(subMap_, constructMap_, Pstream::msgType())
+                schedule(subMap_, constructMap_, Pstream::msgType(), comm_)
             )
         );
     }
@@ -200,9 +220,12 @@ void Foam::mapDistributeBase::checkReceivedSize
 
 void Foam::mapDistributeBase::printLayout(Ostream& os) const
 {
+    const label myRank = Pstream::myProcNo(comm_);
+    const label nProcs = Pstream::nProcs(comm_);
+
     // Determine offsets of remote data.
-    labelList minIndex(Pstream::nProcs(), labelMax);
-    labelList maxIndex(Pstream::nProcs(), labelMin);
+    labelList minIndex(nProcs, labelMax);
+    labelList maxIndex(nProcs, labelMin);
     forAll(constructMap_, proci)
     {
         const labelList& construct = constructMap_[proci];
@@ -227,27 +250,27 @@ void Foam::mapDistributeBase::printLayout(Ostream& os) const
     }
 
     label localSize;
-    if (maxIndex[Pstream::myProcNo()] == labelMin)
+    if (maxIndex[myRank] == labelMin)
     {
         localSize = 0;
     }
     else
     {
-        localSize = maxIndex[Pstream::myProcNo()]+1;
+        localSize = maxIndex[myRank]+1;
     }
 
     os  << "Layout: (constructSize:" << constructSize_
         << " subHasFlip:" << subHasFlip_
         << " constructHasFlip:" << constructHasFlip_
         << ")" << endl
-        << "local (processor " << Pstream::myProcNo() << "):" << endl
+        << "local (processor " << myRank << "):" << endl
         << "    start : 0" << endl
         << "    size  : " << localSize << endl;
 
     label offset = localSize;
     forAll(minIndex, proci)
     {
-        if (proci != Pstream::myProcNo())
+        if (proci != myRank)
         {
             if (constructMap_[proci].size() > 0)
             {
@@ -279,10 +302,13 @@ void Foam::mapDistributeBase::calcCompactAddressing
     List<Map<label>>& compactMap
 ) const
 {
-    compactMap.setSize(Pstream::nProcs());
+    const label myRank = Pstream::myProcNo(comm_);
+    const label nProcs = Pstream::nProcs(comm_);
+
+    compactMap.setSize(nProcs);
 
     // Count all (non-local) elements needed. Just for presizing map.
-    labelList nNonLocal(Pstream::nProcs(), Zero);
+    labelList nNonLocal(nProcs, Zero);
 
     for (const label globalIdx : elements)
     {
@@ -296,7 +322,7 @@ void Foam::mapDistributeBase::calcCompactAddressing
     forAll(compactMap, proci)
     {
         compactMap[proci].clear();
-        if (proci != Pstream::myProcNo())
+        if (proci != myRank)
         {
             compactMap[proci].resize(2*nNonLocal[proci]);
         }
@@ -324,10 +350,13 @@ void Foam::mapDistributeBase::calcCompactAddressing
     List<Map<label>>& compactMap
 ) const
 {
-    compactMap.setSize(Pstream::nProcs());
+    const label myRank = Pstream::myProcNo(comm_);
+    const label nProcs = Pstream::nProcs(comm_);
+
+    compactMap.setSize(nProcs);
 
     // Count all (non-local) elements needed. Just for presizing map.
-    labelList nNonLocal(Pstream::nProcs(), Zero);
+    labelList nNonLocal(nProcs, Zero);
 
     for (const labelList& cCells : cellCells)
     {
@@ -344,7 +373,7 @@ void Foam::mapDistributeBase::calcCompactAddressing
     forAll(compactMap, proci)
     {
         compactMap[proci].clear();
-        if (proci != Pstream::myProcNo())
+        if (proci != myRank)
         {
             compactMap[proci].resize(2*nNonLocal[proci]);
         }
@@ -377,16 +406,19 @@ void Foam::mapDistributeBase::exchangeAddressing
     labelList& compactStart
 )
 {
+    const label myRank = Pstream::myProcNo(comm_);
+    const label nProcs = Pstream::nProcs(comm_);
+
     // The overall compact addressing is
     // - myProcNo data first (uncompacted)
     // - all other processors consecutively
 
-    compactStart.setSize(Pstream::nProcs());
-    compactStart[Pstream::myProcNo()] = 0;
+    compactStart.setSize(nProcs);
+    compactStart[myRank] = 0;
     constructSize_ = globalNumbering.localSize();
     forAll(compactStart, proci)
     {
-        if (proci != Pstream::myProcNo())
+        if (proci != myRank)
         {
             compactStart[proci] = constructSize_;
             constructSize_ += compactMap[proci].size();
@@ -398,12 +430,12 @@ void Foam::mapDistributeBase::exchangeAddressing
     // Find out what to receive/send in compact addressing.
 
     // What I want to receive is what others have to send
-    labelListList wantedRemoteElements(Pstream::nProcs());
+    labelListList wantedRemoteElements(nProcs);
     // Compact addressing for received data
-    constructMap_.setSize(Pstream::nProcs());
+    constructMap_.setSize(nProcs);
     forAll(compactMap, proci)
     {
-        if (proci == Pstream::myProcNo())
+        if (proci == myRank)
         {
             // All my own elements are used
             label nLocal = globalNumbering.localSize();
@@ -429,13 +461,13 @@ void Foam::mapDistributeBase::exchangeAddressing
         }
     }
 
-    subMap_.setSize(Pstream::nProcs());
+    subMap_.setSize(nProcs);
     Pstream::exchange<labelList, label>
     (
         wantedRemoteElements,
         subMap_,
         tag,
-        Pstream::worldComm  //TBD
+        comm_
     );
 
     // Renumber elements
@@ -455,16 +487,19 @@ void Foam::mapDistributeBase::exchangeAddressing
     labelList& compactStart
 )
 {
+    const label myRank = Pstream::myProcNo(comm_);
+    const label nProcs = Pstream::nProcs(comm_);
+
     // The overall compact addressing is
     // - myProcNo data first (uncompacted)
     // - all other processors consecutively
 
-    compactStart.setSize(Pstream::nProcs());
-    compactStart[Pstream::myProcNo()] = 0;
+    compactStart.setSize(nProcs);
+    compactStart[myRank] = 0;
     constructSize_ = globalNumbering.localSize();
     forAll(compactStart, proci)
     {
-        if (proci != Pstream::myProcNo())
+        if (proci != myRank)
         {
             compactStart[proci] = constructSize_;
             constructSize_ += compactMap[proci].size();
@@ -475,12 +510,12 @@ void Foam::mapDistributeBase::exchangeAddressing
     // Find out what to receive/send in compact addressing.
 
     // What I want to receive is what others have to send
-    labelListList wantedRemoteElements(Pstream::nProcs());
+    labelListList wantedRemoteElements(nProcs);
     // Compact addressing for received data
-    constructMap_.setSize(Pstream::nProcs());
+    constructMap_.setSize(nProcs);
     forAll(compactMap, proci)
     {
-        if (proci == Pstream::myProcNo())
+        if (proci == myRank)
         {
             // All my own elements are used
             label nLocal = globalNumbering.localSize();
@@ -506,13 +541,13 @@ void Foam::mapDistributeBase::exchangeAddressing
         }
     }
 
-    subMap_.setSize(Pstream::nProcs());
+    subMap_.setSize(nProcs);
     Pstream::exchange<labelList, label>
     (
         wantedRemoteElements,
         subMap_,
         tag,
-        Pstream::worldComm      //TBD
+        comm_
     );
 
     // Renumber elements
@@ -528,11 +563,12 @@ void Foam::mapDistributeBase::exchangeAddressing
 
 // * * * * * * * * * * * * * * * * Constructors  * * * * * * * * * * * * * * //
 
-Foam::mapDistributeBase::mapDistributeBase()
+Foam::mapDistributeBase::mapDistributeBase(const label comm)
 :
     constructSize_(0),
     subHasFlip_(false),
     constructHasFlip_(false),
+    comm_(comm),
     schedulePtr_()
 {}
 
@@ -545,6 +581,7 @@ Foam::mapDistributeBase::mapDistributeBase(const mapDistributeBase& map)
     constructMap_(map.constructMap_),
     subHasFlip_(map.subHasFlip_),
     constructHasFlip_(map.constructHasFlip_),
+    comm_(map.comm_),
     schedulePtr_()
 {}
 
@@ -563,7 +600,8 @@ Foam::mapDistributeBase::mapDistributeBase
     labelListList&& subMap,
     labelListList&& constructMap,
     const bool subHasFlip,
-    const bool constructHasFlip
+    const bool constructHasFlip,
+    const label comm
 )
 :
     constructSize_(constructSize),
@@ -571,6 +609,7 @@ Foam::mapDistributeBase::mapDistributeBase
     constructMap_(std::move(constructMap)),
     subHasFlip_(subHasFlip),
     constructHasFlip_(constructHasFlip),
+    comm_(comm),
     schedulePtr_()
 {}
 
@@ -578,14 +617,19 @@ Foam::mapDistributeBase::mapDistributeBase
 Foam::mapDistributeBase::mapDistributeBase
 (
     const labelUList& sendProcs,
-    const labelUList& recvProcs
+    const labelUList& recvProcs,
+    const label comm
 )
 :
     constructSize_(0),
     subHasFlip_(false),
     constructHasFlip_(false),
+    comm_(comm),
     schedulePtr_()
 {
+    const label myRank = Pstream::myProcNo(comm_);
+    const label nProcs = Pstream::nProcs(comm_);
+
     if (sendProcs.size() != recvProcs.size())
     {
         FatalErrorInFunction
@@ -595,8 +639,8 @@ Foam::mapDistributeBase::mapDistributeBase
     }
 
     // Per processor the number of samples we have to send/receive.
-    labelList nSend(Pstream::nProcs(), Zero);
-    labelList nRecv(Pstream::nProcs(), Zero);
+    labelList nSend(nProcs, Zero);
+    labelList nRecv(nProcs, Zero);
 
     forAll(sendProcs, sampleI)
     {
@@ -606,20 +650,20 @@ Foam::mapDistributeBase::mapDistributeBase
         // Note that also need to include local communication (both
         // RecvProc and sendProc on local processor)
 
-        if (Pstream::myProcNo() == sendProc)
+        if (myRank == sendProc)
         {
             // I am the sender. Count destination processor.
             nSend[recvProc]++;
         }
-        if (Pstream::myProcNo() == recvProc)
+        if (myRank == recvProc)
         {
             // I am the receiver.
             nRecv[sendProc]++;
         }
     }
 
-    subMap_.setSize(Pstream::nProcs());
-    constructMap_.setSize(Pstream::nProcs());
+    subMap_.setSize(nProcs);
+    constructMap_.setSize(nProcs);
     forAll(nSend, proci)
     {
         subMap_[proci].setSize(nSend[proci]);
@@ -633,12 +677,12 @@ Foam::mapDistributeBase::mapDistributeBase
         const label sendProc = sendProcs[sampleI];
         const label recvProc = recvProcs[sampleI];
 
-        if (Pstream::myProcNo() == sendProc)
+        if (myRank == sendProc)
         {
             // I am the sender. Store index I need to send.
             subMap_[recvProc][nSend[recvProc]++] = sampleI;
         }
-        if (Pstream::myProcNo() == recvProc)
+        if (myRank == recvProc)
         {
             // I am the receiver.
             constructMap_[sendProc][nRecv[sendProc]++] = sampleI;
@@ -654,12 +698,14 @@ Foam::mapDistributeBase::mapDistributeBase
     const globalIndex& globalNumbering,
     labelList& elements,
     List<Map<label>>& compactMap,
-    const int tag
+    const int tag,
+    const label comm
 )
 :
     constructSize_(0),
     subHasFlip_(false),
     constructHasFlip_(false),
+    comm_(comm),
     schedulePtr_()
 {
     // Construct per processor compact addressing of the global elements
@@ -675,7 +721,7 @@ Foam::mapDistributeBase::mapDistributeBase
     //// Sort remote elements needed (not really necessary)
     //forAll(compactMap, proci)
     //{
-    //    if (proci != Pstream::myProcNo())
+    //    if (proci != myRank)
     //    {
     //        Map<label>& globalMap = compactMap[proci];
     //
@@ -713,12 +759,14 @@ Foam::mapDistributeBase::mapDistributeBase
     const globalIndex& globalNumbering,
     labelListList& cellCells,
     List<Map<label>>& compactMap,
-    const int tag
+    const int tag,
+    const label comm
 )
 :
     constructSize_(0),
     subHasFlip_(false),
     constructHasFlip_(false),
+    comm_(comm),
     schedulePtr_()
 {
     // Construct per processor compact addressing of the global elements
@@ -734,7 +782,7 @@ Foam::mapDistributeBase::mapDistributeBase
     //// Sort remote elements needed (not really necessary)
     //forAll(compactMap, proci)
     //{
-    //    if (proci != Pstream::myProcNo())
+    //    if (proci != myRank)
     //    {
     //        Map<label>& globalMap = compactMap[proci];
     //
@@ -771,26 +819,31 @@ Foam::mapDistributeBase::mapDistributeBase
 (
     labelListList&& subMap,
     const bool subHasFlip,
-    const bool constructHasFlip
+    const bool constructHasFlip,
+    const label comm
 )
 :
     constructSize_(0),
     subMap_(std::move(subMap)),
     subHasFlip_(subHasFlip),
     constructHasFlip_(constructHasFlip),
+    comm_(comm),
     schedulePtr_()
 {
+    const label myRank = Pstream::myProcNo(comm_);
+    const label nProcs = Pstream::nProcs(comm_);
+
     // Send over how many i need to receive.
     labelList recvSizes;
-    Pstream::exchangeSizes(subMap_, recvSizes);
+    Pstream::exchangeSizes(subMap_, recvSizes, comm_);
 
     // Determine order of receiving
-    labelListList constructMap(Pstream::nProcs());
+    labelListList constructMap(nProcs);
 
     // My local segments first
-    label nLocal = recvSizes[Pstream::myProcNo()];
+    label nLocal = recvSizes[myRank];
     {
-        labelList& myMap = constructMap[Pstream::myProcNo()];
+        labelList& myMap = constructMap[myRank];
         myMap.setSize(nLocal);
         forAll(myMap, i)
         {
@@ -801,7 +854,7 @@ Foam::mapDistributeBase::mapDistributeBase
     label segmenti = nLocal;
     forAll(constructMap, proci)
     {
-        if (proci != Pstream::myProcNo())
+        if (proci != myRank)
         {
             // What i need to receive is what other processor is sending to me.
             label nRecv = recvSizes[proci];
@@ -840,6 +893,7 @@ void Foam::mapDistributeBase::transfer(mapDistributeBase& rhs)
     constructMap_.transfer(rhs.constructMap_);
     subHasFlip_ = rhs.subHasFlip_;
     constructHasFlip_ = rhs.constructHasFlip_;
+    comm_ = rhs.comm_;
     schedulePtr_.clear();
 
     rhs.constructSize_ = 0;
@@ -872,8 +926,15 @@ Foam::label Foam::mapDistributeBase::renumber
 }
 
 
-void Foam::mapDistributeBase::compact(const boolList& elemIsUsed, const int tag)
+void Foam::mapDistributeBase::compact
+(
+    const boolList& elemIsUsed,
+    const int tag
+)
 {
+    const label myRank = Pstream::myProcNo(comm_);
+    const label nProcs = Pstream::nProcs(comm_);
+
     // 1. send back to sender. Have sender delete the corresponding element
     //    from the submap and do the same to the constructMap locally
     //    (and in same order).
@@ -886,13 +947,13 @@ void Foam::mapDistributeBase::compact(const boolList& elemIsUsed, const int tag)
 
         // Set up receives from neighbours
 
-        List<boolList> recvFields(Pstream::nProcs());
+        List<boolList> recvFields(nProcs);
 
-        for (const int domain : Pstream::allProcs())
+        for (const int domain : Pstream::allProcs(comm_))
         {
             const labelList& map = subMap_[domain];
 
-            if (domain != Pstream::myProcNo() && map.size())
+            if (domain != myRank && map.size())
             {
                 recvFields[domain].setSize(map.size());
                 IPstream::read
@@ -901,19 +962,20 @@ void Foam::mapDistributeBase::compact(const boolList& elemIsUsed, const int tag)
                     domain,
                     reinterpret_cast<char*>(recvFields[domain].data()),
                     recvFields[domain].size()*sizeof(bool),
-                    tag
+                    tag,
+                    comm_
                 );
             }
         }
 
 
-        List<boolList> sendFields(Pstream::nProcs());
+        List<boolList> sendFields(nProcs);
 
-        for (const int domain : Pstream::allProcs())
+        for (const int domain : Pstream::allProcs(comm_))
         {
             const labelList& map = constructMap_[domain];
 
-            if (domain != Pstream::myProcNo() && map.size())
+            if (domain != myRank && map.size())
             {
                 boolList& subField = sendFields[domain];
                 subField.setSize(map.size());
@@ -934,7 +996,8 @@ void Foam::mapDistributeBase::compact(const boolList& elemIsUsed, const int tag)
                     domain,
                     reinterpret_cast<const char*>(subField.cdata()),
                     subField.size()*sizeof(bool),
-                    tag
+                    tag,
+                    comm_
                 );
             }
         }
@@ -944,12 +1007,12 @@ void Foam::mapDistributeBase::compact(const boolList& elemIsUsed, const int tag)
         // Set up 'send' to myself - write directly into recvFields
 
         {
-            const labelList& map = constructMap_[Pstream::myProcNo()];
+            const labelList& map = constructMap_[myRank];
 
-            recvFields[Pstream::myProcNo()].setSize(map.size());
+            recvFields[myRank].setSize(map.size());
             forAll(map, i)
             {
-                recvFields[Pstream::myProcNo()][i] = accessAndFlip
+                recvFields[myRank][i] = accessAndFlip
                 (
                     elemIsUsed,
                     map[i],
@@ -966,7 +1029,7 @@ void Foam::mapDistributeBase::compact(const boolList& elemIsUsed, const int tag)
 
 
         // Compact out all submap entries that are referring to unused elements
-        for (const int domain : Pstream::allProcs())
+        for (const int domain : Pstream::allProcs(comm_))
         {
             const labelList& map = subMap_[domain];
 
@@ -995,7 +1058,7 @@ void Foam::mapDistributeBase::compact(const boolList& elemIsUsed, const int tag)
 
     label maxConstructIndex = -1;
 
-    for (const int domain : Pstream::allProcs())
+    for (const int domain : Pstream::allProcs(comm_))
     {
         const labelList& map = constructMap_[domain];
 
@@ -1041,6 +1104,9 @@ void Foam::mapDistributeBase::compact
     const int tag
 )
 {
+    const label myRank = Pstream::myProcNo(comm_);
+    const label nProcs = Pstream::nProcs(comm_);
+
     // 1. send back to sender. Have sender delete the corresponding element
     //    from the submap and do the same to the constructMap locally
     //    (and in same order).
@@ -1053,13 +1119,13 @@ void Foam::mapDistributeBase::compact
 
         // Set up receives from neighbours
 
-        List<boolList> recvFields(Pstream::nProcs());
+        List<boolList> recvFields(nProcs);
 
-        for (const int domain : Pstream::allProcs())
+        for (const int domain : Pstream::allProcs(comm_))
         {
             const labelList& map = subMap_[domain];
 
-            if (domain != Pstream::myProcNo() && map.size())
+            if (domain != myRank && map.size())
             {
                 recvFields[domain].setSize(map.size());
                 IPstream::read
@@ -1068,19 +1134,20 @@ void Foam::mapDistributeBase::compact
                     domain,
                     reinterpret_cast<char*>(recvFields[domain].data()),
                     recvFields[domain].size()*sizeof(bool),
-                    tag
+                    tag,
+                    comm_
                 );
             }
         }
 
 
-        List<boolList> sendFields(Pstream::nProcs());
+        List<boolList> sendFields(nProcs);
 
-        for (const int domain : Pstream::allProcs())
+        for (const int domain : Pstream::allProcs(comm_))
         {
             const labelList& map = constructMap_[domain];
 
-            if (domain != Pstream::myProcNo() && map.size())
+            if (domain != myRank && map.size())
             {
                 boolList& subField = sendFields[domain];
                 subField.setSize(map.size());
@@ -1100,7 +1167,8 @@ void Foam::mapDistributeBase::compact
                     domain,
                     reinterpret_cast<const char*>(subField.cdata()),
                     subField.size()*sizeof(bool),
-                    tag
+                    tag,
+                    comm_
                 );
             }
         }
@@ -1110,9 +1178,9 @@ void Foam::mapDistributeBase::compact
         // Set up 'send' to myself - write directly into recvFields
 
         {
-            const labelList& map = constructMap_[Pstream::myProcNo()];
+            const labelList& map = constructMap_[myRank];
 
-            recvFields[Pstream::myProcNo()].setSize(map.size());
+            recvFields[myRank].setSize(map.size());
             forAll(map, i)
             {
                 label index = map[i];
@@ -1120,7 +1188,7 @@ void Foam::mapDistributeBase::compact
                 {
                     index = mag(index)-1;
                 }
-                recvFields[Pstream::myProcNo()][i] = elemIsUsed[index];
+                recvFields[myRank][i] = elemIsUsed[index];
             }
         }
 
@@ -1138,7 +1206,7 @@ void Foam::mapDistributeBase::compact
 
             boolList sendElemIsUsed(localSize, false);
 
-            for (const int domain : Pstream::allProcs())
+            for (const int domain : Pstream::allProcs(comm_))
             {
                 const labelList& map = subMap_[domain];
                 forAll(map, i)
@@ -1167,7 +1235,7 @@ void Foam::mapDistributeBase::compact
 
 
         // Compact out all submap entries that are referring to unused elements
-        for (const int domain : Pstream::allProcs())
+        for (const int domain : Pstream::allProcs(comm_))
         {
             const labelList& map = subMap_[domain];
 
@@ -1217,7 +1285,7 @@ void Foam::mapDistributeBase::compact
         }
     }
 
-    for (const int domain : Pstream::allProcs())
+    for (const int domain : Pstream::allProcs(comm_))
     {
         const labelList& map = constructMap_[domain];
 
@@ -1268,6 +1336,7 @@ void Foam::mapDistributeBase::operator=(const mapDistributeBase& rhs)
     constructMap_ = rhs.constructMap_;
     subHasFlip_ = rhs.subHasFlip_;
     constructHasFlip_ = rhs.constructHasFlip_;
+    comm_ = rhs.comm_;
     schedulePtr_.clear();
 }
 
@@ -1289,7 +1358,8 @@ Foam::Istream& Foam::operator>>(Istream& is, mapDistributeBase& map)
     is.fatalCheck(FUNCTION_NAME);
 
     is  >> map.constructSize_ >> map.subMap_ >> map.constructMap_
-        >> map.subHasFlip_ >> map.constructHasFlip_;
+        >> map.subHasFlip_ >> map.constructHasFlip_
+        >> map.comm_;
 
     return is;
 }
@@ -1303,7 +1373,7 @@ Foam::Ostream& Foam::operator<<(Ostream& os, const mapDistributeBase& map)
         << map.subMap_ << token::NL
         << map.constructMap_ << token::NL
         << map.subHasFlip_ << token::SPACE << map.constructHasFlip_
-        << token::NL;
+        << token::SPACE << map.comm_ << token::NL;
 
     return os;
 }
diff --git a/src/OpenFOAM/meshes/polyMesh/mapPolyMesh/mapDistribute/mapDistributeBase.H b/src/OpenFOAM/meshes/polyMesh/mapPolyMesh/mapDistribute/mapDistributeBase.H
index 020fe2edf6..64d99e4fc1 100644
--- a/src/OpenFOAM/meshes/polyMesh/mapPolyMesh/mapDistribute/mapDistributeBase.H
+++ b/src/OpenFOAM/meshes/polyMesh/mapPolyMesh/mapDistribute/mapDistributeBase.H
@@ -122,6 +122,8 @@ protected:
         //- Whether constructMap includes flip or not
         bool constructHasFlip_;
 
+        //- Communicator to use for parallel operations
+        label comm_;
 
         //- Schedule
         mutable autoPtr<List<labelPair>> schedulePtr_;
@@ -199,7 +201,7 @@ public:
     // Constructors
 
         //- Construct null
-        mapDistributeBase();
+        mapDistributeBase(const label comm = UPstream::worldComm);
 
         //- Copy construct
         mapDistributeBase(const mapDistributeBase& map);
@@ -214,7 +216,8 @@ public:
             labelListList&& subMap,
             labelListList&& constructMap,
             const bool subHasFlip = false,
-            const bool constructHasFlip = false
+            const bool constructHasFlip = false,
+            const label comm = UPstream::worldComm
         );
 
         //- Construct from reverse addressing: per data item the send
@@ -223,7 +226,8 @@ public:
         mapDistributeBase
         (
             const labelUList& sendProcs,
-            const labelUList& recvProcs
+            const labelUList& recvProcs,
+            const label comm = UPstream::worldComm
         );
 
         //- Construct from list of (possibly) remote elements in globalIndex
@@ -235,7 +239,8 @@ public:
             const globalIndex&,
             labelList& elements,
             List<Map<label>>& compactMap,
-            const int tag = Pstream::msgType()
+            const int tag = Pstream::msgType(),
+            const label comm = UPstream::worldComm
         );
 
         //- Special variant that works with the info sorted into bins
@@ -246,7 +251,8 @@ public:
             const globalIndex&,
             labelListList& cellCells,
             List<Map<label>>& compactMap,
-            const int tag = Pstream::msgType()
+            const int tag = Pstream::msgType(),
+            const label comm = UPstream::worldComm
         );
 
         //- Construct from my elements to send. Assumes layout is my elements
@@ -256,7 +262,8 @@ public:
         (
             labelListList&& subMap,
             const bool subHasFlip = false,
-            const bool constructHasFlip = false
+            const bool constructHasFlip = false,
+            const label comm = UPstream::worldComm
         );
 
         //- Construct from Istream
@@ -327,12 +334,18 @@ public:
                 return constructHasFlip_;
             }
 
+            label comm() const
+            {
+                return comm_;
+            }
+
             //- Calculate a schedule. See above.
             static List<labelPair> schedule
             (
                 const labelListList& subMap,
                 const labelListList& constructMap,
-                const int tag
+                const int tag,
+                const label comm = UPstream::worldComm
             );
 
             //- Return a schedule. Demand driven. See above.
@@ -389,7 +402,8 @@ public:
                 const bool constructHasFlip,
                 List<T>&,
                 const negateOp& negOp,
-                const int tag = UPstream::msgType()
+                const int tag = UPstream::msgType(),
+                const label comm = UPstream::worldComm
             );
 
             //- Distribute data. If multiple processors writing to same
@@ -405,10 +419,11 @@ public:
                 const labelListList& constructMap,
                 const bool constructHasFlip,
                 List<T>&,
+                const T& nullValue,
                 const CombineOp& cop,
                 const negateOp& negOp,
-                const T& nullValue,
-                const int tag = UPstream::msgType()
+                const int tag = UPstream::msgType(),
+                const label comm = UPstream::worldComm
             );
 
             //- Distribute data using default commsType.
diff --git a/src/OpenFOAM/meshes/polyMesh/mapPolyMesh/mapDistribute/mapDistributeBaseTemplates.C b/src/OpenFOAM/meshes/polyMesh/mapPolyMesh/mapDistribute/mapDistributeBaseTemplates.C
index e9f9ebccd5..43c2e6c29a 100644
--- a/src/OpenFOAM/meshes/polyMesh/mapPolyMesh/mapDistribute/mapDistributeBaseTemplates.C
+++ b/src/OpenFOAM/meshes/polyMesh/mapPolyMesh/mapDistribute/mapDistributeBaseTemplates.C
@@ -129,14 +129,18 @@ void Foam::mapDistributeBase::distribute
     const bool constructHasFlip,
     List<T>& field,
     const negateOp& negOp,
-    const int tag
+    const int tag,
+    const label comm
 )
 {
+    const label myRank = Pstream::myProcNo(comm);
+    const label nProcs = Pstream::nProcs(comm);
+
     if (!Pstream::parRun())
     {
         // Do only me to me.
 
-        const labelList& mySubMap = subMap[Pstream::myProcNo()];
+        const labelList& mySubMap = subMap[myRank];
 
         List<T> subField(mySubMap.size());
         forAll(mySubMap, i)
@@ -145,7 +149,7 @@ void Foam::mapDistributeBase::distribute
         }
 
         // Receive sub field from myself (subField)
-        const labelList& map = constructMap[Pstream::myProcNo()];
+        const labelList& map = constructMap[myRank];
 
         field.setSize(constructSize);
 
@@ -168,13 +172,20 @@ void Foam::mapDistributeBase::distribute
         // received data.
 
         // Send sub field to neighbour
-        for (const int domain : Pstream::allProcs())
+        for (const int domain : Pstream::allProcs(comm))
         {
             const labelList& map = subMap[domain];
 
-            if (domain != Pstream::myProcNo() && map.size())
+            if (domain != myRank && map.size())
             {
-                OPstream toNbr(Pstream::commsTypes::blocking, domain, 0, tag);
+                OPstream toNbr
+                (
+                    Pstream::commsTypes::blocking,
+                    domain,
+                    0,
+                    tag,
+                    comm
+                );
 
                 List<T> subField(map.size());
                 forAll(subField, i)
@@ -192,7 +203,7 @@ void Foam::mapDistributeBase::distribute
         }
 
         // Subset myself
-        const labelList& mySubMap = subMap[Pstream::myProcNo()];
+        const labelList& mySubMap = subMap[myRank];
 
         List<T> subField(mySubMap.size());
         forAll(mySubMap, i)
@@ -201,7 +212,7 @@ void Foam::mapDistributeBase::distribute
         }
 
         // Receive sub field from myself (subField)
-        const labelList& map = constructMap[Pstream::myProcNo()];
+        const labelList& map = constructMap[myRank];
 
         field.setSize(constructSize);
 
@@ -216,13 +227,20 @@ void Foam::mapDistributeBase::distribute
         );
 
         // Receive sub field from neighbour
-        for (const int domain : Pstream::allProcs())
+        for (const int domain : Pstream::allProcs(comm))
         {
             const labelList& map = constructMap[domain];
 
-            if (domain != Pstream::myProcNo() && map.size())
+            if (domain != myRank && map.size())
             {
-                IPstream fromNbr(Pstream::commsTypes::blocking, domain, 0, tag);
+                IPstream fromNbr
+                (
+                    Pstream::commsTypes::blocking,
+                    domain,
+                    0,
+                    tag,
+                    comm
+                );
                 List<T> subField(fromNbr);
 
                 checkReceivedSize(domain, map.size(), subField.size());
@@ -248,7 +266,7 @@ void Foam::mapDistributeBase::distribute
 
         // Receive sub field from myself
         {
-            const labelList& mySubMap = subMap[Pstream::myProcNo()];
+            const labelList& mySubMap = subMap[myRank];
 
             List<T> subField(mySubMap.size());
             forAll(subField, i)
@@ -265,7 +283,7 @@ void Foam::mapDistributeBase::distribute
             // Receive sub field from myself (subField)
             flipAndCombine
             (
-                constructMap[Pstream::myProcNo()],
+                constructMap[myRank],
                 constructHasFlip,
                 subField,
                 eqOp<T>(),
@@ -284,7 +302,7 @@ void Foam::mapDistributeBase::distribute
             label sendProc = twoProcs[0];
             label recvProc = twoProcs[1];
 
-            if (Pstream::myProcNo() == sendProc)
+            if (myRank == sendProc)
             {
                 // I am send first, receive next
                 {
@@ -293,7 +311,8 @@ void Foam::mapDistributeBase::distribute
                         Pstream::commsTypes::scheduled,
                         recvProc,
                         0,
-                        tag
+                        tag,
+                        comm
                     );
 
                     const labelList& map = subMap[recvProc];
@@ -316,7 +335,8 @@ void Foam::mapDistributeBase::distribute
                         Pstream::commsTypes::scheduled,
                         recvProc,
                         0,
-                        tag
+                        tag,
+                        comm
                     );
                     List<T> subField(fromNbr);
 
@@ -344,7 +364,8 @@ void Foam::mapDistributeBase::distribute
                         Pstream::commsTypes::scheduled,
                         sendProc,
                         0,
-                        tag
+                        tag,
+                        comm
                     );
                     List<T> subField(fromNbr);
 
@@ -368,7 +389,8 @@ void Foam::mapDistributeBase::distribute
                         Pstream::commsTypes::scheduled,
                         sendProc,
                         0,
-                        tag
+                        tag,
+                        comm
                     );
 
                     const labelList& map = subMap[sendProc];
@@ -395,14 +417,14 @@ void Foam::mapDistributeBase::distribute
 
         if (!is_contiguous<T>::value)
         {
-            PstreamBuffers pBufs(Pstream::commsTypes::nonBlocking, tag);
+            PstreamBuffers pBufs(Pstream::commsTypes::nonBlocking, tag, comm);
 
             // Stream data into buffer
-            for (const int domain : Pstream::allProcs())
+            for (const int domain : Pstream::allProcs(comm))
             {
                 const labelList& map = subMap[domain];
 
-                if (domain != Pstream::myProcNo() && map.size())
+                if (domain != myRank && map.size())
                 {
                     // Put data into send buffer
                     UOPstream toDomain(domain, pBufs);
@@ -427,7 +449,7 @@ void Foam::mapDistributeBase::distribute
 
             {
                 // Set up 'send' to myself
-                const labelList& mySub = subMap[Pstream::myProcNo()];
+                const labelList& mySub = subMap[myRank];
                 List<T> mySubField(mySub.size());
                 forAll(mySub, i)
                 {
@@ -443,7 +465,7 @@ void Foam::mapDistributeBase::distribute
                 field.setSize(constructSize);
                 // Receive sub field from myself
                 {
-                    const labelList& map = constructMap[Pstream::myProcNo()];
+                    const labelList& map = constructMap[myRank];
 
                     flipAndCombine
                     (
@@ -461,11 +483,11 @@ void Foam::mapDistributeBase::distribute
             Pstream::waitRequests(nOutstanding);
 
             // Consume
-            for (const int domain : Pstream::allProcs())
+            for (const int domain : Pstream::allProcs(comm))
             {
                 const labelList& map = constructMap[domain];
 
-                if (domain != Pstream::myProcNo() && map.size())
+                if (domain != myRank && map.size())
                 {
                     UIPstream str(domain, pBufs);
                     List<T> recvField(str);
@@ -488,13 +510,13 @@ void Foam::mapDistributeBase::distribute
         {
             // Set up sends to neighbours
 
-            List<List<T>> sendFields(Pstream::nProcs());
+            List<List<T>> sendFields(nProcs);
 
-            for (const int domain : Pstream::allProcs())
+            for (const int domain : Pstream::allProcs(comm))
             {
                 const labelList& map = subMap[domain];
 
-                if (domain != Pstream::myProcNo() && map.size())
+                if (domain != myRank && map.size())
                 {
                     List<T>& subField = sendFields[domain];
                     subField.setSize(map.size());
@@ -515,20 +537,21 @@ void Foam::mapDistributeBase::distribute
                         domain,
                         reinterpret_cast<const char*>(subField.cdata()),
                         subField.byteSize(),
-                        tag
+                        tag,
+                        comm
                     );
                 }
             }
 
             // Set up receives from neighbours
 
-            List<List<T>> recvFields(Pstream::nProcs());
+            List<List<T>> recvFields(nProcs);
 
-            for (const int domain : Pstream::allProcs())
+            for (const int domain : Pstream::allProcs(comm))
             {
                 const labelList& map = constructMap[domain];
 
-                if (domain != Pstream::myProcNo() && map.size())
+                if (domain != myRank && map.size())
                 {
                     recvFields[domain].setSize(map.size());
                     IPstream::read
@@ -537,7 +560,8 @@ void Foam::mapDistributeBase::distribute
                         domain,
                         reinterpret_cast<char*>(recvFields[domain].data()),
                         recvFields[domain].byteSize(),
-                        tag
+                        tag,
+                        comm
                     );
                 }
             }
@@ -546,9 +570,9 @@ void Foam::mapDistributeBase::distribute
             // Set up 'send' to myself
 
             {
-                const labelList& map = subMap[Pstream::myProcNo()];
+                const labelList& map = subMap[myRank];
 
-                List<T>& subField = sendFields[Pstream::myProcNo()];
+                List<T>& subField = sendFields[myRank];
                 subField.setSize(map.size());
                 forAll(map, i)
                 {
@@ -568,10 +592,10 @@ void Foam::mapDistributeBase::distribute
             field.setSize(constructSize);
 
 
-            // Receive sub field from myself (sendFields[Pstream::myProcNo()])
+            // Receive sub field from myself (sendFields[myRank])
             {
-                const labelList& map = constructMap[Pstream::myProcNo()];
-                const List<T>& subField = sendFields[Pstream::myProcNo()];
+                const labelList& map = constructMap[myRank];
+                const List<T>& subField = sendFields[myRank];
 
                 flipAndCombine
                 (
@@ -592,11 +616,11 @@ void Foam::mapDistributeBase::distribute
 
             // Collect neighbour fields
 
-            for (const int domain : Pstream::allProcs())
+            for (const int domain : Pstream::allProcs(comm))
             {
                 const labelList& map = constructMap[domain];
 
-                if (domain != Pstream::myProcNo() && map.size())
+                if (domain != myRank && map.size())
                 {
                     const List<T>& subField = recvFields[domain];
 
@@ -636,17 +660,21 @@ void Foam::mapDistributeBase::distribute
     const labelListList& constructMap,
     const bool constructHasFlip,
     List<T>& field,
+    const T& nullValue,
     const CombineOp& cop,
     const negateOp& negOp,
-    const T& nullValue,
-    const int tag
+    const int tag,
+    const label comm
 )
 {
+    const label myRank = Pstream::myProcNo(comm);
+    const label nProcs = Pstream::nProcs(comm);
+
     if (!Pstream::parRun())
     {
         // Do only me to me.
 
-        const labelList& mySubMap = subMap[Pstream::myProcNo()];
+        const labelList& mySubMap = subMap[myRank];
 
         List<T> subField(mySubMap.size());
         forAll(mySubMap, i)
@@ -655,7 +683,7 @@ void Foam::mapDistributeBase::distribute
         }
 
         // Receive sub field from myself (subField)
-        const labelList& map = constructMap[Pstream::myProcNo()];
+        const labelList& map = constructMap[myRank];
 
         field.setSize(constructSize);
         field = nullValue;
@@ -671,13 +699,20 @@ void Foam::mapDistributeBase::distribute
         // received data.
 
         // Send sub field to neighbour
-        for (const int domain : Pstream::allProcs())
+        for (const int domain : Pstream::allProcs(comm))
         {
             const labelList& map = subMap[domain];
 
-            if (domain != Pstream::myProcNo() && map.size())
+            if (domain != myRank && map.size())
             {
-                OPstream toNbr(Pstream::commsTypes::blocking, domain, 0, tag);
+                OPstream toNbr
+                (
+                    Pstream::commsTypes::blocking,
+                    domain,
+                    0,
+                    tag,
+                    comm
+                );
                 List<T> subField(map.size());
                 forAll(subField, i)
                 {
@@ -694,7 +729,7 @@ void Foam::mapDistributeBase::distribute
         }
 
         // Subset myself
-        const labelList& mySubMap = subMap[Pstream::myProcNo()];
+        const labelList& mySubMap = subMap[myRank];
 
         List<T> subField(mySubMap.size());
         forAll(mySubMap, i)
@@ -703,7 +738,7 @@ void Foam::mapDistributeBase::distribute
         }
 
         // Receive sub field from myself (subField)
-        const labelList& map = constructMap[Pstream::myProcNo()];
+        const labelList& map = constructMap[myRank];
 
         field.setSize(constructSize);
         field = nullValue;
@@ -711,13 +746,20 @@ void Foam::mapDistributeBase::distribute
         flipAndCombine(map, constructHasFlip, subField, cop, negOp, field);
 
         // Receive sub field from neighbour
-        for (const int domain : Pstream::allProcs())
+        for (const int domain : Pstream::allProcs(comm))
         {
             const labelList& map = constructMap[domain];
 
-            if (domain != Pstream::myProcNo() && map.size())
+            if (domain != myRank && map.size())
             {
-                IPstream fromNbr(Pstream::commsTypes::blocking, domain, 0, tag);
+                IPstream fromNbr
+                (
+                    Pstream::commsTypes::blocking,
+                    domain,
+                    0,
+                    tag,
+                    comm
+                );
                 List<T> subField(fromNbr);
 
                 checkReceivedSize(domain, map.size(), subField.size());
@@ -742,7 +784,7 @@ void Foam::mapDistributeBase::distribute
         List<T> newField(constructSize, nullValue);
 
         {
-            const labelList& mySubMap = subMap[Pstream::myProcNo()];
+            const labelList& mySubMap = subMap[myRank];
 
             // Subset myself
             List<T> subField(mySubMap.size());
@@ -758,7 +800,7 @@ void Foam::mapDistributeBase::distribute
             }
 
             // Receive sub field from myself (subField)
-            const labelList& map = constructMap[Pstream::myProcNo()];
+            const labelList& map = constructMap[myRank];
 
             flipAndCombine
             (
@@ -782,7 +824,7 @@ void Foam::mapDistributeBase::distribute
             label sendProc = twoProcs[0];
             label recvProc = twoProcs[1];
 
-            if (Pstream::myProcNo() == sendProc)
+            if (myRank == sendProc)
             {
                 // I am send first, receive next
                 {
@@ -791,7 +833,8 @@ void Foam::mapDistributeBase::distribute
                         Pstream::commsTypes::scheduled,
                         recvProc,
                         0,
-                        tag
+                        tag,
+                        comm
                     );
 
                     const labelList& map = subMap[recvProc];
@@ -815,7 +858,8 @@ void Foam::mapDistributeBase::distribute
                         Pstream::commsTypes::scheduled,
                         recvProc,
                         0,
-                        tag
+                        tag,
+                        comm
                     );
                     List<T> subField(fromNbr);
                     const labelList& map = constructMap[recvProc];
@@ -842,7 +886,8 @@ void Foam::mapDistributeBase::distribute
                         Pstream::commsTypes::scheduled,
                         sendProc,
                         0,
-                        tag
+                        tag,
+                        comm
                     );
                     List<T> subField(fromNbr);
                     const labelList& map = constructMap[sendProc];
@@ -865,7 +910,8 @@ void Foam::mapDistributeBase::distribute
                         Pstream::commsTypes::scheduled,
                         sendProc,
                         0,
-                        tag
+                        tag,
+                        comm
                     );
 
                     const labelList& map = subMap[sendProc];
@@ -893,14 +939,14 @@ void Foam::mapDistributeBase::distribute
 
         if (!is_contiguous<T>::value)
         {
-            PstreamBuffers pBufs(Pstream::commsTypes::nonBlocking, tag);
+            PstreamBuffers pBufs(Pstream::commsTypes::nonBlocking, tag, comm);
 
             // Stream data into buffer
-            for (const int domain : Pstream::allProcs())
+            for (const int domain : Pstream::allProcs(comm))
             {
                 const labelList& map = subMap[domain];
 
-                if (domain != Pstream::myProcNo() && map.size())
+                if (domain != myRank && map.size())
                 {
                     // Put data into send buffer
                     UOPstream toDomain(domain, pBufs);
@@ -925,7 +971,7 @@ void Foam::mapDistributeBase::distribute
 
             {
                 // Set up 'send' to myself
-                const labelList& myMap = subMap[Pstream::myProcNo()];
+                const labelList& myMap = subMap[myRank];
 
                 List<T> mySubField(myMap.size());
                 forAll(myMap, i)
@@ -944,7 +990,7 @@ void Foam::mapDistributeBase::distribute
                 field = nullValue;
                 // Receive sub field from myself
                 {
-                    const labelList& map = constructMap[Pstream::myProcNo()];
+                    const labelList& map = constructMap[myRank];
 
                     flipAndCombine
                     (
@@ -962,11 +1008,11 @@ void Foam::mapDistributeBase::distribute
             Pstream::waitRequests(nOutstanding);
 
             // Consume
-            for (const int domain : Pstream::allProcs())
+            for (const int domain : Pstream::allProcs(comm))
             {
                 const labelList& map = constructMap[domain];
 
-                if (domain != Pstream::myProcNo() && map.size())
+                if (domain != myRank && map.size())
                 {
                     UIPstream str(domain, pBufs);
                     List<T> recvField(str);
@@ -989,13 +1035,13 @@ void Foam::mapDistributeBase::distribute
         {
             // Set up sends to neighbours
 
-            List<List<T>> sendFields(Pstream::nProcs());
+            List<List<T>> sendFields(nProcs);
 
-            for (const int domain : Pstream::allProcs())
+            for (const int domain : Pstream::allProcs(comm))
             {
                 const labelList& map = subMap[domain];
 
-                if (domain != Pstream::myProcNo() && map.size())
+                if (domain != myRank && map.size())
                 {
                     List<T>& subField = sendFields[domain];
                     subField.setSize(map.size());
@@ -1016,20 +1062,21 @@ void Foam::mapDistributeBase::distribute
                         domain,
                         reinterpret_cast<const char*>(subField.cdata()),
                         subField.size()*sizeof(T),
-                        tag
+                        tag,
+                        comm
                     );
                 }
             }
 
             // Set up receives from neighbours
 
-            List<List<T>> recvFields(Pstream::nProcs());
+            List<List<T>> recvFields(nProcs);
 
-            for (const int domain : Pstream::allProcs())
+            for (const int domain : Pstream::allProcs(comm))
             {
                 const labelList& map = constructMap[domain];
 
-                if (domain != Pstream::myProcNo() && map.size())
+                if (domain != myRank && map.size())
                 {
                     recvFields[domain].setSize(map.size());
                     UIPstream::read
@@ -1038,7 +1085,8 @@ void Foam::mapDistributeBase::distribute
                         domain,
                         reinterpret_cast<char*>(recvFields[domain].data()),
                         recvFields[domain].size()*sizeof(T),
-                        tag
+                        tag,
+                        comm
                     );
                 }
             }
@@ -1046,9 +1094,9 @@ void Foam::mapDistributeBase::distribute
             // Set up 'send' to myself
 
             {
-                const labelList& map = subMap[Pstream::myProcNo()];
+                const labelList& map = subMap[myRank];
 
-                List<T>& subField = sendFields[Pstream::myProcNo()];
+                List<T>& subField = sendFields[myRank];
                 subField.setSize(map.size());
                 forAll(map, i)
                 {
@@ -1070,8 +1118,8 @@ void Foam::mapDistributeBase::distribute
 
             // Receive sub field from myself (subField)
             {
-                const labelList& map = constructMap[Pstream::myProcNo()];
-                const List<T>& subField = sendFields[Pstream::myProcNo()];
+                const labelList& map = constructMap[myRank];
+                const List<T>& subField = sendFields[myRank];
 
                 flipAndCombine
                 (
@@ -1092,11 +1140,11 @@ void Foam::mapDistributeBase::distribute
 
             // Collect neighbour fields
 
-            for (const int domain : Pstream::allProcs())
+            for (const int domain : Pstream::allProcs(comm))
             {
                 const labelList& map = constructMap[domain];
 
-                if (domain != Pstream::myProcNo() && map.size())
+                if (domain != myRank && map.size())
                 {
                     const List<T>& subField = recvFields[domain];
 
@@ -1129,7 +1177,7 @@ void Foam::mapDistributeBase::send(PstreamBuffers& pBufs, const List<T>& field)
 const
 {
     // Stream data into buffer
-    for (const int domain : Pstream::allProcs())
+    for (const int domain : Pstream::allProcs(comm_))
     {
         const labelList& map = subMap_[domain];
 
@@ -1165,7 +1213,7 @@ const
     // Consume
     field.setSize(constructSize_);
 
-    for (const int domain : Pstream::allProcs())
+    for (const int domain : Pstream::allProcs(comm_))
     {
         const labelList& map = constructMap_[domain];
 
@@ -1219,7 +1267,8 @@ void Foam::mapDistributeBase::distribute
             constructHasFlip_,
             fld,
             negOp,
-            tag
+            tag,
+            comm_
         );
     }
     else if (Pstream::defaultCommsType == Pstream::commsTypes::scheduled)
@@ -1235,7 +1284,8 @@ void Foam::mapDistributeBase::distribute
             constructHasFlip_,
             fld,
             negOp,
-            tag
+            tag,
+            comm_
         );
     }
     else
@@ -1251,7 +1301,8 @@ void Foam::mapDistributeBase::distribute
             constructHasFlip_,
             fld,
             negOp,
-            tag
+            tag,
+            comm_
         );
     }
 }
@@ -1309,7 +1360,8 @@ void Foam::mapDistributeBase::reverseDistribute
             subHasFlip_,
             fld,
             flipOp(),
-            tag
+            tag,
+            comm_
         );
     }
     else if (Pstream::defaultCommsType == Pstream::commsTypes::scheduled)
@@ -1325,7 +1377,8 @@ void Foam::mapDistributeBase::reverseDistribute
             subHasFlip_,
             fld,
             flipOp(),
-            tag
+            tag,
+            comm_
         );
     }
     else
@@ -1341,7 +1394,8 @@ void Foam::mapDistributeBase::reverseDistribute
             subHasFlip_,
             fld,
             flipOp(),
-            tag
+            tag,
+            comm_
         );
     }
 }
@@ -1371,10 +1425,11 @@ void Foam::mapDistributeBase::reverseDistribute
             subMap_,
             subHasFlip_,
             fld,
+            nullValue,
             eqOp<T>(),
             flipOp(),
-            nullValue,
-            tag
+            tag,
+            comm_
         );
     }
     else if (Pstream::defaultCommsType == Pstream::commsTypes::scheduled)
@@ -1389,10 +1444,11 @@ void Foam::mapDistributeBase::reverseDistribute
             subMap_,
             subHasFlip_,
             fld,
+            nullValue,
             eqOp<T>(),
             flipOp(),
-            nullValue,
-            tag
+            tag,
+            comm_
         );
     }
     else
@@ -1407,10 +1463,11 @@ void Foam::mapDistributeBase::reverseDistribute
             subMap_,
             subHasFlip_,
             fld,
+            nullValue,
             eqOp<T>(),
             flipOp(),
-            nullValue,
-            tag
+            tag,
+            comm_
         );
     }
 }
diff --git a/src/Pstream/mpi/UPstream.C b/src/Pstream/mpi/UPstream.C
index 9eb2f37073..0964e754cc 100644
--- a/src/Pstream/mpi/UPstream.C
+++ b/src/Pstream/mpi/UPstream.C
@@ -245,16 +245,46 @@ bool Foam::UPstream::init(int& argc, char**& argv, const bool needsThread)
         ourMpi = true;
     }
 
+    // Check argument list for local world
+    label worldIndex = -1;
+    word world;
+    for (int argi = 1; argi < argc; ++argi)
+    {
+        if (strcmp(argv[argi], "-world") == 0)
+        {
+            worldIndex = argi++;
+            if (argi >= argc)
+            {
+                FatalErrorInFunction
+                    << "Missing world name to argument \"world\""
+                    << Foam::abort(FatalError);
+            }
+            world = argv[argi];
+            break;
+        }
+    }
+
+    // Filter 'world' option
+    if (worldIndex != -1)
+    {
+        for (label i = worldIndex+2; i < argc; i++)
+        {
+            argv[i-2] = argv[i];
+        }
+        argc -= 2;
+    }
+
     MPI_Comm_size(MPI_COMM_WORLD, &numprocs);
     MPI_Comm_rank(MPI_COMM_WORLD, &myRank);
 
     if (debug)
     {
-        Pout<< "UPstream::init : procs=" << numprocs
-            << " rank:" << myRank << endl;
+        Pout<< "UPstream::init : procs:" << numprocs
+            << " rank:" << myRank
+            << " world:" << world << endl;
     }
 
-    if (numprocs <= 1)
+    if (worldIndex == -1 && numprocs <= 1)
     {
         FatalErrorInFunction
             << "attempt to run parallel on 1 processor"
@@ -264,6 +294,85 @@ bool Foam::UPstream::init(int& argc, char**& argv, const bool needsThread)
     // Initialise parallel structure
     setParRun(numprocs, provided_thread_support == MPI_THREAD_MULTIPLE);
 
+    if (worldIndex != -1)
+    {
+        wordList worlds(numprocs);
+        worlds[Pstream::myProcNo()] = world;
+        Pstream::gatherList(worlds);
+        Pstream::scatterList(worlds);
+
+        // Compact
+        if (Pstream::master())
+        {
+            DynamicList<word> allWorlds(numprocs);
+            for (const auto& world : worlds)
+            {
+                if (!allWorlds.found(world))
+                {
+                    allWorlds.append(world);
+                }
+            }
+            allWorlds_ = std::move(allWorlds);
+
+            worldIDs_.setSize(numprocs);
+            forAll(worlds, proci)
+            {
+                const word& world = worlds[proci];
+                worldIDs_[proci] = allWorlds_.find(world);
+            }
+        }
+        Pstream::scatter(allWorlds_);
+        Pstream::scatter(worldIDs_);
+
+        DynamicList<label> subRanks;
+        forAll(worlds, proci)
+        {
+            if (worlds[proci] == worlds[Pstream::myProcNo()])
+            {
+                subRanks.append(proci);
+            }
+        }
+
+        // Allocate new communicator 1 with parent 0 (= mpi_world)
+        const label subComm = allocateCommunicator(0, subRanks, true);
+
+        // Override worldComm
+        UPstream::worldComm = subComm;
+        // For testing: warn use of non-worldComm
+        UPstream::warnComm = UPstream::worldComm;
+
+        if (debug)
+        {
+            // Check
+            int subNProcs, subRank;
+            MPI_Comm_size
+            (
+                PstreamGlobals::MPICommunicators_[subComm],
+                &subNProcs
+            );
+            MPI_Comm_rank
+            (
+                PstreamGlobals::MPICommunicators_[subComm],
+                &subRank
+            );
+
+            Pout<< "UPstream::init : in world:" << world
+                << " using local communicator:" << subComm
+                << " with procs:" << subNProcs
+                << " and rank:" << subRank
+                << endl;
+        }
+
+        // Override Pout prefix (move to setParRun?)
+        Pout.prefix() = '[' + world + '/' +  name(myProcNo(subComm)) + "] ";
+        Perr.prefix() = '[' + world + '/' +  name(myProcNo(subComm)) + "] ";
+    }
+    else
+    {
+        // All processors use world 0
+        worldIDs_.setSize(numprocs, 0);
+    }
+
     attachOurBuffers();
 
     return true;
@@ -357,6 +466,7 @@ void Foam::UPstream::shutdown(int errNo)
         }
         else
         {
+            // Abort only locally or world?
             MPI_Abort(MPI_COMM_WORLD, errNo);
         }
     }
@@ -443,7 +553,7 @@ void Foam::sumReduce
 {
     if (UPstream::warnComm != -1 && communicator != UPstream::warnComm)
     {
-        Pout<< "** reducing:" << Value << " with comm:" << communicator
+        Pout<< "** sumReduce:" << Value << " with comm:" << communicator
             << " warnComm:" << UPstream::warnComm
             << endl;
         error::printStack(Pout);
@@ -623,7 +733,18 @@ void Foam::UPstream::allToAll
     const label communicator
 )
 {
-    label np = nProcs(communicator);
+    const label np = nProcs(communicator);
+
+    if (UPstream::warnComm != -1 && communicator != UPstream::warnComm)
+    {
+        Pout<< "** allToAll :"
+            << " np:" << np
+            << " sendData:" << sendData.size()
+            << " with comm:" << communicator
+            << " warnComm:" << UPstream::warnComm
+            << endl;
+        error::printStack(Pout);
+    }
 
     if (sendData.size() != np || recvData.size() != np)
     {
@@ -683,7 +804,18 @@ void Foam::UPstream::allToAll
     const label communicator
 )
 {
-    label np = nProcs(communicator);
+    const label np = nProcs(communicator);
+
+    if (UPstream::warnComm != -1 && communicator != UPstream::warnComm)
+    {
+        Pout<< "** allToAll :"
+            << " sendSizes:" << sendSizes
+            << " sendOffsets:" << sendOffsets
+            << " with comm:" << communicator
+            << " warnComm:" << UPstream::warnComm
+            << endl;
+        error::printStack(Pout);
+    }
 
     if
     (
@@ -757,7 +889,19 @@ void Foam::UPstream::gather
     const label communicator
 )
 {
-    label np = nProcs(communicator);
+    const label np = nProcs(communicator);
+
+    if (UPstream::warnComm != -1 && communicator != UPstream::warnComm)
+    {
+        Pout<< "** allToAll :"
+            << " np:" << np
+            << " recvSizes:" << recvSizes
+            << " recvOffsets:" << recvOffsets
+            << " with comm:" << communicator
+            << " warnComm:" << UPstream::warnComm
+            << endl;
+        error::printStack(Pout);
+    }
 
     if
     (
@@ -823,7 +967,19 @@ void Foam::UPstream::scatter
     const label communicator
 )
 {
-    label np = nProcs(communicator);
+    const label np = nProcs(communicator);
+
+    if (UPstream::warnComm != -1 && communicator != UPstream::warnComm)
+    {
+        Pout<< "** allToAll :"
+            << " np:" << np
+            << " sendSizes:" << sendSizes
+            << " sendOffsets:" << sendOffsets
+            << " with comm:" << communicator
+            << " warnComm:" << UPstream::warnComm
+            << endl;
+        error::printStack(Pout);
+    }
 
     if
     (
@@ -976,7 +1132,7 @@ void Foam::UPstream::allocatePstreamCommunicator
 
 void Foam::UPstream::freePstreamCommunicator(const label communicator)
 {
-    if (communicator != UPstream::worldComm)
+    if (communicator != 0)
     {
         if (PstreamGlobals::MPICommunicators_[communicator] != MPI_COMM_NULL)
         {
diff --git a/src/TurbulenceModels/compressible/turbulentFluidThermoModels/derivedFvPatchFields/turbulentTemperatureCoupledBaffleMixed/turbulentTemperatureCoupledBaffleMixedFvPatchScalarField.C b/src/TurbulenceModels/compressible/turbulentFluidThermoModels/derivedFvPatchFields/turbulentTemperatureCoupledBaffleMixed/turbulentTemperatureCoupledBaffleMixedFvPatchScalarField.C
index 96dd7905de..e1506f058c 100644
--- a/src/TurbulenceModels/compressible/turbulentFluidThermoModels/derivedFvPatchFields/turbulentTemperatureCoupledBaffleMixed/turbulentTemperatureCoupledBaffleMixedFvPatchScalarField.C
+++ b/src/TurbulenceModels/compressible/turbulentFluidThermoModels/derivedFvPatchFields/turbulentTemperatureCoupledBaffleMixed/turbulentTemperatureCoupledBaffleMixedFvPatchScalarField.C
@@ -6,7 +6,7 @@
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
     Copyright (C) 2011-2016 OpenFOAM Foundation
-    Copyright (C) 2019 OpenCFD Ltd.
+    Copyright (C) 2019-2020 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -57,6 +57,11 @@ turbulentTemperatureCoupledBaffleMixedFvPatchScalarField
         "undefined-K",
         "undefined-alpha"
     ),
+    mappedPatchFieldBase<scalar>
+    (
+        mappedPatchFieldBase<scalar>::mapper(p, iF),
+        *this
+    ),
     TnbrName_("undefined-Tnbr"),
     thicknessLayers_(0),
     kappaLayers_(0),
@@ -79,6 +84,12 @@ turbulentTemperatureCoupledBaffleMixedFvPatchScalarField
 :
     mixedFvPatchScalarField(ptf, p, iF, mapper),
     temperatureCoupledBase(patch(), ptf),
+    mappedPatchFieldBase<scalar>
+    (
+        mappedPatchFieldBase<scalar>::mapper(p, iF),
+        *this,
+        ptf
+    ),
     TnbrName_(ptf.TnbrName_),
     thicknessLayers_(ptf.thicknessLayers_),
     kappaLayers_(ptf.kappaLayers_),
@@ -96,21 +107,17 @@ turbulentTemperatureCoupledBaffleMixedFvPatchScalarField
 :
     mixedFvPatchScalarField(p, iF),
     temperatureCoupledBase(patch(), dict),
+    mappedPatchFieldBase<scalar>
+    (
+        mappedPatchFieldBase<scalar>::mapper(p, iF),
+        *this,
+        dict
+    ),
     TnbrName_(dict.get<word>("Tnbr")),
     thicknessLayers_(0),
     kappaLayers_(0),
     contactRes_(0.0)
 {
-    if (!isA<mappedPatchBase>(this->patch().patch()))
-    {
-        FatalErrorInFunction
-            << "' not type '" << mappedPatchBase::typeName << "'"
-            << "\n    for patch " << p.name()
-            << " of field " << internalField().name()
-            << " in file " << internalField().objectPath()
-            << exit(FatalError);
-    }
-
     if (dict.readIfPresent("thicknessLayers", thicknessLayers_))
     {
         dict.readEntry("kappaLayers", kappaLayers_);
@@ -142,6 +149,18 @@ turbulentTemperatureCoupledBaffleMixedFvPatchScalarField
         refGrad() = 0.0;
         valueFraction() = 1.0;
     }
+
+    // Store patch value as initial guess when running in database mode
+    mappedPatchFieldBase<scalar>::initRetrieveField
+    (
+        this->internalField().name(),
+        *this
+    );
+    mappedPatchFieldBase<scalar>::initRetrieveField
+    (
+        this->internalField().name() + "_weights",
+        this->patch().deltaCoeffs()
+    );
 }
 
 
@@ -154,6 +173,33 @@ turbulentTemperatureCoupledBaffleMixedFvPatchScalarField
 :
     mixedFvPatchScalarField(wtcsf, iF),
     temperatureCoupledBase(patch(), wtcsf),
+    mappedPatchFieldBase<scalar>
+    (
+        mappedPatchFieldBase<scalar>::mapper(patch(), iF),
+        *this,
+        wtcsf
+    ),
+    TnbrName_(wtcsf.TnbrName_),
+    thicknessLayers_(wtcsf.thicknessLayers_),
+    kappaLayers_(wtcsf.kappaLayers_),
+    contactRes_(wtcsf.contactRes_)
+{}
+
+
+turbulentTemperatureCoupledBaffleMixedFvPatchScalarField::
+turbulentTemperatureCoupledBaffleMixedFvPatchScalarField
+(
+    const turbulentTemperatureCoupledBaffleMixedFvPatchScalarField& wtcsf
+)
+:
+    mixedFvPatchScalarField(wtcsf),
+    temperatureCoupledBase(patch(), wtcsf),
+    mappedPatchFieldBase<scalar>
+    (
+        mappedPatchFieldBase<scalar>::mapper(patch(), wtcsf.internalField()),
+        *this,
+        wtcsf
+    ),
     TnbrName_(wtcsf.TnbrName_),
     thicknessLayers_(wtcsf.thicknessLayers_),
     kappaLayers_(wtcsf.kappaLayers_),
@@ -172,51 +218,89 @@ void turbulentTemperatureCoupledBaffleMixedFvPatchScalarField::updateCoeffs()
 
     // Since we're inside initEvaluate/evaluate there might be processor
     // comms underway. Change the tag we use.
-    int oldTag = UPstream::msgType();
+    const int oldTag = UPstream::msgType();
     UPstream::msgType() = oldTag+1;
 
     // Get the coupling information from the mappedPatchBase
     const mappedPatchBase& mpp =
-        refCast<const mappedPatchBase>(patch().patch());
-    const polyMesh& nbrMesh = mpp.sampleMesh();
-    const label samplePatchi = mpp.samplePolyPatch().index();
-    const fvPatch& nbrPatch =
-        refCast<const fvMesh>(nbrMesh).boundary()[samplePatchi];
-
-    // Calculate the temperature by harmonic averaging
-    // ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-
-    const turbulentTemperatureCoupledBaffleMixedFvPatchScalarField& nbrField =
-    refCast
-    <
-        const turbulentTemperatureCoupledBaffleMixedFvPatchScalarField
-    >
-    (
-        nbrPatch.lookupPatchField<volScalarField, scalar>
+        mappedPatchFieldBase<scalar>::mapper
         (
-            TnbrName_
-        )
-    );
+            patch(),
+            this->internalField()
+        );
 
-    // Swap to obtain full local values of neighbour internal field
-    tmp<scalarField> nbrIntFld(new scalarField(nbrField.size(), Zero));
-    tmp<scalarField> nbrKDelta(new scalarField(nbrField.size(), Zero));
+    const tmp<scalarField> myKDelta = kappa(*this)*patch().deltaCoeffs();
+    tmp<scalarField> nbrIntFld;
+    tmp<scalarField> nbrKDelta;
 
-    if (contactRes_ == 0.0)
+    //Pout<< "updateCoeffs() : mpp.sameWorld():" << mpp.sameWorld() << endl;
+
+
+    if (mpp.sameWorld())
     {
-        nbrIntFld.ref() = nbrField.patchInternalField();
-        nbrKDelta.ref() = nbrField.kappa(nbrField)*nbrPatch.deltaCoeffs();
+        // Same world so lookup
+        const auto& nbrMesh = refCast<const fvMesh>(mpp.sampleMesh());
+        const label nbrPatchID = mpp.samplePolyPatch().index();
+        const auto& nbrPatch = nbrMesh.boundary()[nbrPatchID];
+
+        const turbulentTemperatureCoupledBaffleMixedFvPatchScalarField&
+        nbrField =
+        refCast
+        <
+        const turbulentTemperatureCoupledBaffleMixedFvPatchScalarField
+        >
+        (
+            nbrPatch.lookupPatchField<volScalarField, scalar>
+            (
+                TnbrName_
+            )
+        );
+
+        if (contactRes_ == 0.0)
+        {
+            // Get neighbour internal data in local order. Does all
+            // comms/reordering already
+            nbrIntFld = this->mappedInternalField();
+            // Calculate neighbour weighting (in neighbouring ordering)
+            nbrKDelta = nbrField.kappa(nbrField)*nbrPatch.deltaCoeffs();
+        }
+        else
+        {
+            // Get neighbour patch values
+            nbrIntFld = new scalarField(nbrField);
+            // Comms/reorder to local
+            distribute(this->internalField().name(), nbrIntFld.ref());
+
+            // Constant neighbour weighting. Reorder/comms below
+            nbrKDelta = new scalarField(nbrField.size(), contactRes_);
+        }
     }
     else
     {
-        nbrIntFld.ref() = nbrField;
-        nbrKDelta.ref() = contactRes_;
+        // Different world so use my region,patch. Distribution below will
+        // do the reordering
+        if (contactRes_ == 0.0)
+        {
+            nbrIntFld = this->mappedInternalField();
+            nbrKDelta = new scalarField(myKDelta());
+        }
+        else
+        {
+            nbrIntFld = *this;
+            nbrKDelta = new scalarField(this->size(), contactRes_);
+        }
     }
 
-    mpp.distribute(nbrIntFld.ref());
-    mpp.distribute(nbrKDelta.ref());
 
-    tmp<scalarField> myKDelta = kappa(*this)*patch().deltaCoeffs();
+    //Pout<< "updateCoeffs() : nbrIntFld:" << flatOutput(nbrIntFld()) << endl;
+    //Pout<< "updateCoeffs() : nbrKDelta BEFORE:" << flatOutput(nbrKDelta())
+    //    << endl;
+
+    distribute(this->internalField().name() + "_weights", nbrKDelta.ref());
+    //Pout<< "updateCoeffs() : nbrKDelta AFTER:" << flatOutput(nbrKDelta())
+    //    << endl;
+    //Pout<< "updateCoeffs() : myKDelta:" << flatOutput(myKDelta())
+    //    << endl;
 
 
     // Both sides agree on
@@ -247,8 +331,8 @@ void turbulentTemperatureCoupledBaffleMixedFvPatchScalarField::updateCoeffs()
         Info<< patch().boundaryMesh().mesh().name() << ':'
             << patch().name() << ':'
             << this->internalField().name() << " <- "
-            << nbrMesh.name() << ':'
-            << nbrPatch.name() << ':'
+            << mpp.sampleRegion() << ':'
+            << mpp.samplePatch() << ':'
             << this->internalField().name() << " :"
             << " heat transfer rate:" << Q
             << " walltemperature "
@@ -274,6 +358,7 @@ void turbulentTemperatureCoupledBaffleMixedFvPatchScalarField::write
     kappaLayers_.writeEntry("kappaLayers", os);
 
     temperatureCoupledBase::write(os);
+    mappedPatchFieldBase<scalar>::write(os);
 }
 
 
diff --git a/src/TurbulenceModels/compressible/turbulentFluidThermoModels/derivedFvPatchFields/turbulentTemperatureCoupledBaffleMixed/turbulentTemperatureCoupledBaffleMixedFvPatchScalarField.H b/src/TurbulenceModels/compressible/turbulentFluidThermoModels/derivedFvPatchFields/turbulentTemperatureCoupledBaffleMixed/turbulentTemperatureCoupledBaffleMixedFvPatchScalarField.H
index 926656d40e..358066580c 100644
--- a/src/TurbulenceModels/compressible/turbulentFluidThermoModels/derivedFvPatchFields/turbulentTemperatureCoupledBaffleMixed/turbulentTemperatureCoupledBaffleMixedFvPatchScalarField.H
+++ b/src/TurbulenceModels/compressible/turbulentFluidThermoModels/derivedFvPatchFields/turbulentTemperatureCoupledBaffleMixed/turbulentTemperatureCoupledBaffleMixedFvPatchScalarField.H
@@ -82,6 +82,7 @@ SourceFiles
 
 #include "mixedFvPatchFields.H"
 #include "temperatureCoupledBase.H"
+#include "mappedPatchFieldBase.H"
 #include "scalarField.H"
 
 // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
@@ -98,7 +99,8 @@ namespace compressible
 class turbulentTemperatureCoupledBaffleMixedFvPatchScalarField
 :
     public mixedFvPatchScalarField,
-    public temperatureCoupledBase
+    public temperatureCoupledBase,
+    public mappedPatchFieldBase<scalar>
 {
     // Private data
 
@@ -149,6 +151,12 @@ public:
             const fvPatchFieldMapper&
         );
 
+        //- Construct as copy setting internal field reference
+        turbulentTemperatureCoupledBaffleMixedFvPatchScalarField
+        (
+            const turbulentTemperatureCoupledBaffleMixedFvPatchScalarField&
+        );
+
         //- Construct and return a clone
         virtual tmp<fvPatchScalarField> clone() const
         {
diff --git a/src/finiteVolume/Make/files b/src/finiteVolume/Make/files
index 7ef61600d6..b4db8e8f3b 100644
--- a/src/finiteVolume/Make/files
+++ b/src/finiteVolume/Make/files
@@ -228,8 +228,9 @@ $(derivedFvPatchFields)/plenumPressure/plenumPressureFvPatchScalarField.C
 $(derivedFvPatchFields)/interfaceCompression/interfaceCompressionFvPatchScalarField.C
 $(derivedFvPatchFields)/swirlFanVelocity/swirlFanVelocityFvPatchField.C
 
+$(derivedFvPatchFields)/mappedMixed/mappedMixedFvPatchFields.C
 $(derivedFvPatchFields)/mappedField/Sampled/makeSampledPatchFunction1s.C
-
+$(derivedFvPatchFields)/mappedField/mappedMixedFieldFvPatchField/mappedMixedFieldFvPatchFields.C
 
 fvsPatchFields = fields/fvsPatchFields
 $(fvsPatchFields)/fvsPatchField/fvsPatchFields.C
diff --git a/src/finiteVolume/fields/fvPatchFields/derived/mappedField/mappedFieldFvPatchField.C b/src/finiteVolume/fields/fvPatchFields/derived/mappedField/mappedFieldFvPatchField.C
index d3830bf071..21ad7cdc0a 100644
--- a/src/finiteVolume/fields/fvPatchFields/derived/mappedField/mappedFieldFvPatchField.C
+++ b/src/finiteVolume/fields/fvPatchFields/derived/mappedField/mappedFieldFvPatchField.C
@@ -54,7 +54,7 @@ Foam::mappedFieldFvPatchField<Type>::mappedFieldFvPatchField
 :
     fixedValueFvPatchField<Type>(p, iF, dict),
     mappedPatchBase(p.patch(), dict),
-    mappedPatchFieldBase<Type>(*this, *this, dict)
+    mappedPatchFieldBase<Type>(*this, *this, dict, *this)
 {}
 
 
diff --git a/src/finiteVolume/fields/fvPatchFields/derived/mappedField/mappedMixedFieldFvPatchField/mappedMixedFieldFvPatchField.C b/src/finiteVolume/fields/fvPatchFields/derived/mappedField/mappedMixedFieldFvPatchField/mappedMixedFieldFvPatchField.C
new file mode 100644
index 0000000000..52dae310de
--- /dev/null
+++ b/src/finiteVolume/fields/fvPatchFields/derived/mappedField/mappedMixedFieldFvPatchField/mappedMixedFieldFvPatchField.C
@@ -0,0 +1,233 @@
+/*---------------------------------------------------------------------------*\
+  =========                 |
+  \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
+   \\    /   O peration     |
+    \\  /    A nd           | www.openfoam.com
+     \\/     M anipulation  |
+-------------------------------------------------------------------------------
+    Copyright (C) 2019-2020 OpenCFD Ltd.
+-------------------------------------------------------------------------------
+License
+    This file is part of OpenFOAM.
+
+    OpenFOAM is free software: you can redistribute it and/or modify it
+    under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    OpenFOAM is distributed in the hope that it will be useful, but WITHOUT
+    ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+    FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+    for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with OpenFOAM.  If not, see <http://www.gnu.org/licenses/>.
+
+\*---------------------------------------------------------------------------*/
+
+#include "mappedMixedFieldFvPatchField.H"
+#include "volFields.H"
+#include "interpolationCell.H"
+
+// * * * * * * * * * * * * * * * * Constructors  * * * * * * * * * * * * * * //
+
+template<class Type>
+Foam::mappedMixedFieldFvPatchField<Type>::mappedMixedFieldFvPatchField
+(
+    const fvPatch& p,
+    const DimensionedField<Type, volMesh>& iF
+)
+:
+    mixedFvPatchField<Type>(p, iF),
+    mappedPatchBase(p.patch()),
+    mappedPatchFieldBase<Type>(*this, *this),
+    weightFieldName_(word::null)
+{
+    this->refValue() = Zero;
+    this->refGrad() = Zero;
+    this->valueFraction() = 0.0;
+}
+
+
+template<class Type>
+Foam::mappedMixedFieldFvPatchField<Type>::mappedMixedFieldFvPatchField
+(
+    const fvPatch& p,
+    const DimensionedField<Type, volMesh>& iF,
+    const dictionary& dict
+)
+:
+    mixedFvPatchField<Type>(p, iF, dict),
+    mappedPatchBase(p.patch(), dict),
+    mappedPatchFieldBase<Type>(*this, *this, dict),
+    weightFieldName_(dict.getOrDefault<word>("weightField", word::null))
+{
+    mixedFvPatchField<Type>::operator=
+    (
+        Field<Type>("value", dict, p.size())
+    );
+
+    if (dict.found("refValue"))
+    {
+        // Full restart
+        this->refValue() = Field<Type>("refValue", dict, p.size());
+        this->refGrad() = Field<Type>("refGradient", dict, p.size());
+        this->valueFraction() = scalarField("valueFraction", dict, p.size());
+    }
+    else
+    {
+        // Start from user entered data. Assume fixedValue.
+        this->refValue() = *this;
+        this->refGrad() = Zero;
+        this->valueFraction() = 1.0;
+    }
+
+    // Store patch value as initial guess when running in database mode
+    mappedPatchFieldBase<Type>::initRetrieveField
+    (
+        this->internalField().name(),
+        *this
+    );
+    mappedPatchFieldBase<Type>::initRetrieveField
+    (
+        this->internalField().name() + "_weights",
+        this->patch().deltaCoeffs()
+    );
+}
+
+
+template<class Type>
+Foam::mappedMixedFieldFvPatchField<Type>::mappedMixedFieldFvPatchField
+(
+    const mappedMixedFieldFvPatchField<Type>& ptf,
+    const fvPatch& p,
+    const DimensionedField<Type, volMesh>& iF,
+    const fvPatchFieldMapper& mapper
+)
+:
+    mixedFvPatchField<Type>(ptf, p, iF, mapper),
+    mappedPatchBase(p.patch(), ptf),
+    mappedPatchFieldBase<Type>(*this, *this, ptf),
+    weightFieldName_(ptf.weightFieldName_)
+{}
+
+
+template<class Type>
+Foam::mappedMixedFieldFvPatchField<Type>::mappedMixedFieldFvPatchField
+(
+    const mappedMixedFieldFvPatchField<Type>& ptf
+)
+:
+    mixedFvPatchField<Type>(ptf),
+    mappedPatchBase(ptf.patch().patch(), ptf),
+    mappedPatchFieldBase<Type>(ptf),
+    weightFieldName_(ptf.weightFieldName_)
+{}
+
+
+template<class Type>
+Foam::mappedMixedFieldFvPatchField<Type>::mappedMixedFieldFvPatchField
+(
+    const mappedMixedFieldFvPatchField<Type>& ptf,
+    const DimensionedField<Type, volMesh>& iF
+)
+:
+    mixedFvPatchField<Type>(ptf, iF),
+    mappedPatchBase(ptf.patch().patch(), ptf),
+    mappedPatchFieldBase<Type>(*this, *this, ptf),
+    weightFieldName_(ptf.weightFieldName_)
+{}
+
+
+// * * * * * * * * * * * * * * * Member Functions  * * * * * * * * * * * * * //
+
+template<class Type>
+void Foam::mappedMixedFieldFvPatchField<Type>::autoMap
+(
+    const fvPatchFieldMapper& m
+)
+{
+    mixedFvPatchField<Type>::autoMap(m);
+    mappedPatchBase::clearOut();
+}
+
+
+template<class Type>
+void Foam::mappedMixedFieldFvPatchField<Type>::rmap
+(
+    const fvPatchField<Type>& ptf,
+    const labelList& addr
+)
+{
+    mixedFvPatchField<Type>::rmap(ptf, addr);
+    mappedPatchBase::clearOut();
+}
+
+
+template<class Type>
+void Foam::mappedMixedFieldFvPatchField<Type>::updateCoeffs()
+{
+    if (this->updated())
+    {
+        return;
+    }
+
+    const tmp<Field<Type>> nbrIntFld(this->mappedInternalField());
+
+    //- Unweighted
+    //const tmp<scalarField> nbrKDelta(this->mappedWeightField());
+
+    //- Weighted
+    tmp<scalarField> myKDelta;
+    tmp<scalarField> nbrKDelta;
+    this->mappedWeightField(weightFieldName_, myKDelta, nbrKDelta);
+
+    // Both sides agree on
+    // - temperature : (myKDelta*fld + nbrKDelta*nbrFld)/(myKDelta+nbrKDelta)
+    // - gradient    : (temperature-fld)*delta
+    // We've got a degree of freedom in how to implement this in a mixed bc.
+    // (what gradient, what fixedValue and mixing coefficient)
+    // Two reasonable choices:
+    // 1. specify above temperature on one side (preferentially the high side)
+    //    and above gradient on the other. So this will switch between pure
+    //    fixedvalue and pure fixedgradient
+    // 2. specify gradient and temperature such that the equations are the
+    //    same on both sides. This leads to the choice of
+    //    - refGradient = zero gradient
+    //    - refValue = neighbour value
+    //    - mixFraction = nbrKDelta / (nbrKDelta + myKDelta())
+
+    this->refValue() = nbrIntFld;
+    this->refGrad() = Zero;
+    this->valueFraction() = nbrKDelta()/(nbrKDelta() + myKDelta());
+
+    mixedFvPatchField<Type>::updateCoeffs();
+
+    if (debug)
+    {
+        Info<< this->patch().boundaryMesh().mesh().name() << ':'
+            << this->patch().name() << ':'
+            << this->internalField().name() << " <- "
+            << this->mapper_.sampleRegion() << ':'
+            << this->mapper_.samplePatch() << ':'
+            << this->fieldName_ << " :"
+            << " value "
+            << " min:" << gMin(*this)
+            << " max:" << gMax(*this)
+            << " avg:" << gAverage(*this)
+            << endl;
+    }
+}
+
+
+template<class Type>
+void Foam::mappedMixedFieldFvPatchField<Type>::write(Ostream& os) const
+{
+    mappedPatchBase::write(os);
+    mappedPatchFieldBase<Type>::write(os);
+    os.writeEntryIfDifferent<word>("weightField", word::null, weightFieldName_);
+    mixedFvPatchField<Type>::write(os);
+}
+
+
+// ************************************************************************* //
diff --git a/src/finiteVolume/fields/fvPatchFields/derived/mappedField/mappedMixedFieldFvPatchField/mappedMixedFieldFvPatchField.H b/src/finiteVolume/fields/fvPatchFields/derived/mappedField/mappedMixedFieldFvPatchField/mappedMixedFieldFvPatchField.H
new file mode 100644
index 0000000000..3b6ec90354
--- /dev/null
+++ b/src/finiteVolume/fields/fvPatchFields/derived/mappedField/mappedMixedFieldFvPatchField/mappedMixedFieldFvPatchField.H
@@ -0,0 +1,234 @@
+/*---------------------------------------------------------------------------*\
+  =========                 |
+  \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
+   \\    /   O peration     |
+    \\  /    A nd           | www.openfoam.com
+     \\/     M anipulation  |
+-------------------------------------------------------------------------------
+    Copyright (C) 2019-2020 OpenCFD Ltd.
+-------------------------------------------------------------------------------
+License
+    This file is part of OpenFOAM.
+
+    OpenFOAM is free software: you can redistribute it and/or modify it
+    under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    OpenFOAM is distributed in the hope that it will be useful, but WITHOUT
+    ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+    FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+    for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with OpenFOAM.  If not, see <http://www.gnu.org/licenses/>.
+
+Class
+    Foam::mappedMixedFieldFvPatchField
+
+Group
+    grpGenericBoundaryConditions grpCoupledBoundaryConditions
+
+Description
+    This boundary condition provides a self-contained version of e.g. mapped
+    boundary conditions
+    - it expects two-way coupling (so the sampled field needs to run the
+      same bc)
+    - it does not use information on the patch; instead it holds the coupling
+      data locally.
+
+Usage
+    \table
+        Property     | Description                      | Required | Default
+        field        | Name of field to be mapped       | no  | this field name
+        weightField  | Name of field to use as weight   | no |
+        setAverage   | Use average value                | no  | false |
+        average      | Average value to use if \c setAverage = yes | partly |
+    \endtable
+
+    Example of the boundary condition specification:
+    \verbatim
+    <patchName>
+    {
+        type            mappedMixedField;
+        field           T;              // optional field name
+        setAverage      no;             // apply an average value
+        average         0;              // average to apply if setAverage
+        value           uniform 0;      // place holder
+    }
+    \endverbatim
+
+Note
+    Supports multi-world operation:
+
+    +----+                      +----+
+    |    |                      |    |
+    |    |                      |    |
+    +----+                      +----+
+    worldA                      worldB
+    regionA                     regionB
+    patchA                      patchB
+
+
+See also
+    Foam::mappedPatchBase
+    Foam::mappedPolyPatch
+    Foam::mappedFvPatch
+    Foam::mappedFieldFvPatchField
+    Foam::mixedFvPatchField
+
+SourceFiles
+    mappedMixedFieldFvPatchField.C
+
+\*---------------------------------------------------------------------------*/
+
+#ifndef mappedMixedFieldFvPatchField_H
+#define mappedMixedFieldFvPatchField_H
+
+#include "mappedPatchBase.H"
+#include "mappedPatchFieldBase.H"
+#include "mixedFvPatchFields.H"
+#include "interpolation.H"
+#include "volFieldsFwd.H"
+
+// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
+
+namespace Foam
+{
+
+/*---------------------------------------------------------------------------*\
+                  Class mappedMixedFieldFvPatchField Declaration
+\*---------------------------------------------------------------------------*/
+
+template<class Type>
+class mappedMixedFieldFvPatchField
+:
+    public mixedFvPatchField<Type>,
+    public mappedPatchBase,
+    public mappedPatchFieldBase<Type>
+{
+
+        //- Name of weight field to sample
+        word weightFieldName_;
+
+
+public:
+
+    //- Runtime type information
+    TypeName("mappedMixedField");
+
+
+    // Constructors
+
+        //- Construct from patch and internal field
+        mappedMixedFieldFvPatchField
+        (
+            const fvPatch&,
+            const DimensionedField<Type, volMesh>&
+        );
+
+        //- Construct from patch, internal field and dictionary
+        mappedMixedFieldFvPatchField
+        (
+            const fvPatch&,
+            const DimensionedField<Type, volMesh>&,
+            const dictionary&
+        );
+
+        //- Construct by mapping given
+        //  mappedMixedFieldFvPatchField
+        //  onto a new patch
+        mappedMixedFieldFvPatchField
+        (
+            const mappedMixedFieldFvPatchField<Type>&,
+            const fvPatch&,
+            const DimensionedField<Type, volMesh>&,
+            const fvPatchFieldMapper&
+        );
+
+        //- Construct as copy
+        mappedMixedFieldFvPatchField
+        (
+            const mappedMixedFieldFvPatchField<Type>&
+        );
+
+        //- Construct and return a clone
+        virtual tmp<fvPatchField<Type>> clone() const
+        {
+            return tmp<fvPatchField<Type>>
+            (
+                new mappedMixedFieldFvPatchField<Type>
+                (
+                    *this
+                )
+            );
+        }
+
+        //- Construct as copy setting internal field reference
+        mappedMixedFieldFvPatchField
+        (
+            const mappedMixedFieldFvPatchField<Type>&,
+            const DimensionedField<Type, volMesh>&
+        );
+
+        //- Construct and return a clone setting internal field reference
+        virtual tmp<fvPatchField<Type>> clone
+        (
+            const DimensionedField<Type, volMesh>& iF
+        ) const
+        {
+            return tmp<fvPatchField<Type>>
+            (
+                new mappedMixedFieldFvPatchField<Type>
+                (
+                    *this,
+                    iF
+                )
+            );
+        }
+
+
+    // Member functions
+
+        // Mapping functions
+
+            //- Map (and resize as needed) from self given a mapping object
+            virtual void autoMap
+            (
+                const fvPatchFieldMapper&
+            );
+
+            //- Reverse map the given fvPatchField onto this fvPatchField
+            virtual void rmap
+            (
+                const fvPatchField<Type>&,
+                const labelList&
+            );
+
+
+        // Evaluation functions
+
+            //- Update the coefficients associated with the patch field
+            virtual void updateCoeffs();
+
+
+        //- Write
+        virtual void write(Ostream&) const;
+};
+
+
+// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
+
+} // End namespace Foam
+
+// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
+
+#ifdef NoRepository
+    #include "mappedMixedFieldFvPatchField.C"
+#endif
+
+// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
+
+#endif
+
+// ************************************************************************* //
diff --git a/src/finiteVolume/fields/fvPatchFields/derived/mappedField/mappedMixedFieldFvPatchField/mappedMixedFieldFvPatchFields.C b/src/finiteVolume/fields/fvPatchFields/derived/mappedField/mappedMixedFieldFvPatchField/mappedMixedFieldFvPatchFields.C
new file mode 100644
index 0000000000..e2ff66464a
--- /dev/null
+++ b/src/finiteVolume/fields/fvPatchFields/derived/mappedField/mappedMixedFieldFvPatchField/mappedMixedFieldFvPatchFields.C
@@ -0,0 +1,44 @@
+/*---------------------------------------------------------------------------*\
+  =========                 |
+  \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
+   \\    /   O peration     |
+    \\  /    A nd           | Copyright (C) 2019 OpenCFD Ltd.
+     \\/     M anipulation  |
+-------------------------------------------------------------------------------
+License
+    This file is part of OpenFOAM.
+
+    OpenFOAM is free software: you can redistribute it and/or modify it
+    under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    OpenFOAM is distributed in the hope that it will be useful, but WITHOUT
+    ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+    FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+    for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with OpenFOAM.  If not, see <http://www.gnu.org/licenses/>.
+
+\*---------------------------------------------------------------------------*/
+
+#include "mappedMixedFieldFvPatchFields.H"
+#include "volMesh.H"
+#include "addToRunTimeSelectionTable.H"
+
+// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
+
+namespace Foam
+{
+
+// * * * * * * * * * * * * * * Static Data Members * * * * * * * * * * * * * //
+
+//makeTemplatePatchTypeField(scalar, mappedMixedField);
+makePatchFields(mappedMixedField);
+
+// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
+
+} // End namespace Foam
+
+// ************************************************************************* //
diff --git a/src/finiteVolume/fields/fvPatchFields/derived/mappedField/mappedMixedFieldFvPatchField/mappedMixedFieldFvPatchFields.H b/src/finiteVolume/fields/fvPatchFields/derived/mappedField/mappedMixedFieldFvPatchField/mappedMixedFieldFvPatchFields.H
new file mode 100644
index 0000000000..78d5da4211
--- /dev/null
+++ b/src/finiteVolume/fields/fvPatchFields/derived/mappedField/mappedMixedFieldFvPatchField/mappedMixedFieldFvPatchFields.H
@@ -0,0 +1,51 @@
+/*---------------------------------------------------------------------------*\
+  =========                 |
+  \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
+   \\    /   O peration     |
+    \\  /    A nd           | Copyright (C) 2019 OpenCFD Ltd.
+     \\/     M anipulation  |
+-------------------------------------------------------------------------------
+License
+    This file is part of OpenFOAM.
+
+    OpenFOAM is free software: you can redistribute it and/or modify it
+    under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    OpenFOAM is distributed in the hope that it will be useful, but WITHOUT
+    ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+    FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+    for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with OpenFOAM.  If not, see <http://www.gnu.org/licenses/>.
+
+\*---------------------------------------------------------------------------*/
+
+#ifndef mappedMixedFieldFvPatchFields_H
+#define mappedMixedFieldFvPatchFields_H
+
+#include "mappedMixedFieldFvPatchField.H"
+#include "fieldTypes.H"
+#include "fvPatchFields.H"
+
+// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
+
+namespace Foam
+{
+
+// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
+
+//makePatchTypeFieldTypedef(scalar, mappedMixedField);
+makePatchTypeFieldTypedefs(mappedMixedField)
+
+// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
+
+} // End namespace Foam
+
+// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
+
+#endif
+
+// ************************************************************************* //
diff --git a/src/finiteVolume/fields/fvPatchFields/derived/mappedField/mappedPatchFieldBase.C b/src/finiteVolume/fields/fvPatchFields/derived/mappedField/mappedPatchFieldBase.C
index 6cd627dc7b..d7b9101a62 100644
--- a/src/finiteVolume/fields/fvPatchFields/derived/mappedField/mappedPatchFieldBase.C
+++ b/src/finiteVolume/fields/fvPatchFields/derived/mappedField/mappedPatchFieldBase.C
@@ -48,6 +48,174 @@ Type Foam::mappedPatchFieldBase<Type>::getAverage
 }
 
 
+template<class Type>
+template<class T>
+void Foam::mappedPatchFieldBase<Type>::storeField
+(
+    const objectRegistry& obr,
+    const word& region,
+    const word& patch,
+    const labelListList& procToMap,
+    const word& fieldName,
+    const Field<T>& fld
+) const
+{
+    // Store my data onto database
+    //const label myRank = Pstream::myProcNo(0);  // comm_
+    const label nProcs = Pstream::nProcs(0);    // comm_
+
+    for (label domain = 0; domain < nProcs; domain++)
+    {
+        const labelList& map = procToMap[domain];
+        if (map.size())
+        {
+            const Field<T> subFld(fld, map);
+
+            const objectRegistry& subObr = mappedPatchBase::subRegistry
+            (
+                obr,
+                mapper_.sendPath(domain)
+              / region
+              / patch
+            );
+
+            if (fvPatchField<Type>::debug)
+            {
+                Pout<< "*** STORING :"
+                    << " field:" << fieldName
+                    << " values:" << flatOutput(subFld)
+                    << " as:" << subObr.objectPath() << endl; 
+            }
+
+            mappedPatchBase::storeField
+            (
+                const_cast<objectRegistry&>(subObr),
+                fieldName,
+                subFld
+            );
+        }
+    }
+}
+
+
+template<class Type>
+template<class T>
+void Foam::mappedPatchFieldBase<Type>::retrieveField
+(
+    const bool allowUnset,
+    const objectRegistry& obr,
+    const word& region,
+    const word& patch,
+    const labelListList& procToMap,
+    const word& fieldName,
+    Field<T>& fld
+) const
+{
+    // Store my data onto database
+    //const label myRank = Pstream::myProcNo(0);  // comm_
+    const label nProcs = Pstream::nProcs(0);    // comm_
+
+    for (label domain = 0; domain < nProcs; domain++)
+    {
+        const labelList& map = procToMap[domain];
+        if (map.size())
+        {
+            const objectRegistry& subObr = mappedPatchBase::subRegistry
+            (
+                obr,
+                mapper_.receivePath(domain)
+              / region
+              / patch
+            );
+
+            //const IOField<T>& subFld = subObr.lookupObject<IOField<T>>
+            //(
+            //    fieldName
+            //);
+            const IOField<T>* subFldPtr = subObr.getObjectPtr<IOField<T>>
+            (
+                fieldName
+            );
+            if (subFldPtr)
+            {
+                UIndirectList<T>(fld, map) = *subFldPtr;
+
+                if (fvPatchField<Type>::debug)
+                {
+                    Pout<< "*** RETRIEVED :"
+                        << " field:" << fieldName
+                        << " values:" << flatOutput(fld)
+                        << " from:" << subObr.objectPath() << endl;
+                }
+            }
+            else if (allowUnset)
+            {
+                WarningInFunction << "Not found"
+                    << " field:" << fieldName
+                    << " in:" << subObr.objectPath() << endl;
+            }
+            else
+            {
+                // Not found. Make it fail
+                (void)subObr.lookupObject<IOField<T>>(fieldName);
+            }
+        }
+    }
+}
+
+
+template<class Type>
+template<class T>
+void Foam::mappedPatchFieldBase<Type>::initRetrieveField
+(
+    const objectRegistry& obr,
+    const word& region,
+    const word& patch,
+    const mapDistribute& map,
+    const word& fieldName,
+    const Field<T>& fld
+) const
+{
+    // Store my data onto database
+    //const label myRank = Pstream::myProcNo(0);  // comm_
+    const label nProcs = Pstream::nProcs(0);    // comm_
+
+    for (label domain = 0; domain < nProcs; domain++)
+    {
+        const labelList& constructMap = map.constructMap()[domain];
+        if (constructMap.size())
+        {
+            const objectRegistry& subObr = mappedPatchBase::subRegistry
+            (
+                obr,
+                mapper_.receivePath(domain)
+              / region
+              / patch
+            );
+
+            const Field<T> receiveFld(fld, constructMap);
+
+            if (fvPatchField<Type>::debug)
+            {
+                Pout<< "*** STORING INITIAL :"
+                    << " field:" << fieldName << " values:"
+                    << flatOutput(receiveFld)
+                    << " from:" << flatOutput(fld)
+                    << " constructMap:" << flatOutput(constructMap)
+                    << " as:" << subObr.objectPath() << endl; 
+            }
+
+            mappedPatchBase::storeField
+            (
+                const_cast<objectRegistry&>(subObr),
+                fieldName,
+                receiveFld
+            );
+        }
+    }
+}
+
+
 // * * * * * * * * * * * * * * * * Constructors  * * * * * * * * * * * * * * //
 
 template<class Type>
@@ -92,10 +260,60 @@ Foam::mappedPatchFieldBase<Type>::mappedPatchFieldBase
     average_(getAverage(dict, setAverage_)),
     interpolationScheme_(interpolationCell<Type>::typeName)
 {
+    if
+    (
+        mapper_.sampleDatabase()
+     && mapper_.mode() != mappedPatchBase::NEARESTPATCHFACE
+    )
+    {
+        FatalErrorInFunction
+            << "Mapping using the database only supported for "
+            << "sampleMode "
+            <<  mappedPatchBase::sampleModeNames_
+                [
+                    mappedPatchBase::NEARESTPATCHFACE
+                ]
+            << exit(FatalError);
+    }
+
     if (mapper_.mode() == mappedPatchBase::NEARESTCELL)
     {
         dict.readEntry("interpolationScheme", interpolationScheme_);
     }
+
+    // Note: in database mode derived boundary conditions need to initialise
+    //       fields
+}
+
+
+template<class Type>
+Foam::mappedPatchFieldBase<Type>::mappedPatchFieldBase
+(
+    const mappedPatchBase& mapper,
+    const fvPatchField<Type>& patchField,
+    const dictionary& dict,
+    const Field<Type>& fld
+)
+:
+    mappedPatchFieldBase<Type>::mappedPatchFieldBase(mapper, patchField, dict)
+{
+    if
+    (
+        mapper_.mode() == mappedPatchBase::NEARESTPATCHFACE
+     && mapper_.sampleDatabase()
+    )
+    {
+        // Store my data on receive buffers so we have some initial data
+        initRetrieveField
+        (
+            patchField_.internalField().time(),
+            patchField_.patch().boundaryMesh().mesh().name(),
+            patchField_.patch().name(),
+            mapper_.map(),
+            patchField_.internalField().name(),
+            patchField_
+        );
+    }
 }
 
 
@@ -150,14 +368,15 @@ Foam::mappedPatchFieldBase<Type>::mappedPatchFieldBase
 // * * * * * * * * * * * * * * * Member Functions  * * * * * * * * * * * * * //
 
 template<class Type>
-const Foam::GeometricField<Type, Foam::fvPatchField, Foam::volMesh>&
-Foam::mappedPatchFieldBase<Type>::sampleField() const
+template<class Type2>
+const Foam::GeometricField<Type2, Foam::fvPatchField, Foam::volMesh>&
+Foam::mappedPatchFieldBase<Type>::sampleField(const word& fieldName) const
 {
-    typedef GeometricField<Type, fvPatchField, volMesh> fieldType;
+    typedef GeometricField<Type2, fvPatchField, volMesh> fieldType;
 
     if (mapper_.sameRegion())
     {
-        if (fieldName_ == patchField_.internalField().name())
+        if (fieldName == patchField_.internalField().name())
         {
             // Optimisation: bypass field lookup
             return
@@ -169,18 +388,70 @@ Foam::mappedPatchFieldBase<Type>::sampleField() const
         else
         {
             const fvMesh& thisMesh = patchField_.patch().boundaryMesh().mesh();
-            return thisMesh.template lookupObject<fieldType>(fieldName_);
+            return thisMesh.template lookupObject<fieldType>(fieldName);
         }
     }
 
     const fvMesh& nbrMesh = refCast<const fvMesh>(mapper_.sampleMesh());
-    return nbrMesh.template lookupObject<fieldType>(fieldName_);
+    return nbrMesh.template lookupObject<fieldType>(fieldName);
 }
 
 
 template<class Type>
+const Foam::GeometricField<Type, Foam::fvPatchField, Foam::volMesh>&
+Foam::mappedPatchFieldBase<Type>::sampleField() const
+{
+    return sampleField<Type>(fieldName_);
+}
+
+
+template<class Type>
+template<class T>
+void Foam::mappedPatchFieldBase<Type>::distribute
+(
+    const word& fieldName,
+    Field<T>& newValues
+) const
+{
+    if (mapper_.sampleDatabase())
+    {
+        // Store my data on send buffers
+        storeField
+        (
+            patchField_.internalField().time(),
+            patchField_.patch().boundaryMesh().mesh().name(),
+            patchField_.patch().name(),
+            mapper_.map().subMap(),
+            fieldName,
+            newValues
+        );
+        // Construct my data from receive buffers
+        newValues.setSize(mapper_.map().constructSize());
+        retrieveField
+        (
+            true,                           // allow unset
+            patchField_.internalField().time(),
+            mapper_.sampleRegion(),
+            mapper_.samplePatch(),
+            mapper_.map().constructMap(),
+            fieldName,
+            newValues
+        );
+    }
+    else
+    {
+        mapper_.distribute(newValues);
+    }
+}
+
+
+template<class Type>
+//template<class T>
 Foam::tmp<Foam::Field<Type>>
-Foam::mappedPatchFieldBase<Type>::mappedField() const
+Foam::mappedPatchFieldBase<Type>::mappedField
+(
+//    const GeometricField<T, fvPatchField, volMesh>& fld
+) const
 {
     typedef GeometricField<Type, fvPatchField, volMesh> fieldType;
 
@@ -190,7 +461,6 @@ Foam::mappedPatchFieldBase<Type>::mappedField() const
     UPstream::msgType() = oldTag + 1;
 
     const fvMesh& thisMesh = patchField_.patch().boundaryMesh().mesh();
-    const fvMesh& nbrMesh = refCast<const fvMesh>(mapper_.sampleMesh());
 
     // Result of obtaining remote values
     auto tnewValues = tmp<Field<Type>>::New();
@@ -200,12 +470,25 @@ Foam::mappedPatchFieldBase<Type>::mappedField() const
     {
         case mappedPatchBase::NEARESTCELL:
         {
+            const fieldType& fld = sampleField();
             const mapDistribute& distMap = mapper_.map();
 
             if (interpolationScheme_ != interpolationCell<Type>::typeName)
             {
+                if (!mapper_.sameWorld() || mapper_.sampleDatabase())
+                {
+                    FatalErrorInFunction
+                        << "Interpolating cell values from different world"
+                        << " or database currently not supported"
+                        << exit(FatalError);
+                }
+
+                const fvMesh& nbrMesh =
+                    refCast<const fvMesh>(mapper_.sampleMesh());
+
                 // Send back sample points to the processor that holds the cell
                 vectorField samples(mapper_.samplePoints());
+
                 distMap.reverseDistribute
                 (
                     (
@@ -221,7 +504,7 @@ Foam::mappedPatchFieldBase<Type>::mappedField() const
                     interpolation<Type>::New
                     (
                         interpolationScheme_,
-                        sampleField()
+                        fld
                     );
 
                 const auto& interp = *interpolator;
@@ -241,52 +524,94 @@ Foam::mappedPatchFieldBase<Type>::mappedField() const
             }
             else
             {
-                newValues = sampleField();
+                newValues = fld;
             }
 
-            distMap.distribute(newValues);
+            distribute(fieldName_, newValues);
 
             break;
         }
         case mappedPatchBase::NEARESTPATCHFACE:
         case mappedPatchBase::NEARESTPATCHFACEAMI:
         {
-            const label nbrPatchID =
-                nbrMesh.boundaryMesh().findPatchID(mapper_.samplePatch());
-
-            if (nbrPatchID < 0)
+            if (mapper_.sameWorld())
             {
-                FatalErrorInFunction
-                 << "Unable to find sample patch " << mapper_.samplePatch()
-                 << " in region " << mapper_.sampleRegion()
-                 << " for patch " << patchField_.patch().name() << nl
-                 << abort(FatalError);
+                const fvMesh& nbrMesh =
+                    refCast<const fvMesh>(mapper_.sampleMesh());
+                const fieldType& fld = sampleField();
+
+                const label nbrPatchID =
+                    nbrMesh.boundaryMesh().findPatchID(mapper_.samplePatch());
+
+                if (nbrPatchID < 0)
+                {
+                    FatalErrorInFunction
+                     << "Unable to find sample patch " << mapper_.samplePatch()
+                     << " in region " << mapper_.sampleRegion()
+                     << " for patch " << patchField_.patch().name() << nl
+                     << abort(FatalError);
+                }
+
+                const auto& nbrField = fld;
+
+                newValues = nbrField.boundaryField()[nbrPatchID];
             }
-
-            const fieldType& nbrField = sampleField();
-
-            newValues = nbrField.boundaryField()[nbrPatchID];
-            mapper_.distribute(newValues);
+            else
+            {
+                // Start off from my patch values, let distribute function below
+                // do all the work
+                newValues = patchField_;
+            }
+            distribute(fieldName_, newValues);
 
             break;
         }
         case mappedPatchBase::NEARESTFACE:
         {
-            Field<Type> allValues(nbrMesh.nFaces(), Zero);
-
-            const fieldType& nbrField = sampleField();
-
-            for (const fvPatchField<Type>& pf : nbrField.boundaryField())
+            Field<Type> allValues;
+            if (mapper_.sameWorld())
             {
-                label faceStart = pf.patch().start();
+                const fvMesh& nbrMesh =
+                    refCast<const fvMesh>(mapper_.sampleMesh());
+                const fieldType& fld = sampleField();
 
-                forAll(pf, facei)
+                allValues.setSize(nbrMesh.nFaces(), Zero);
+
+                const auto& nbrField = fld;
+
+                for (const fvPatchField<Type>& pf : nbrField.boundaryField())
                 {
-                    allValues[faceStart++] = pf[facei];
+                    label faceStart = pf.patch().start();
+
+                    forAll(pf, facei)
+                    {
+                        allValues[faceStart++] = pf[facei];
+                    }
+                }
+            }
+            else
+            {
+                // Start off from my patch values. Let distribute function below
+                // do all the work
+                allValues.setSize(thisMesh.nFaces(), Zero);
+
+                const fieldType& thisFld = dynamic_cast<const fieldType&>
+                (
+                    patchField_.internalField()
+                );
+
+                for (const fvPatchField<Type>& pf : thisFld.boundaryField())
+                {
+                    label faceStart = pf.patch().start();
+
+                    forAll(pf, facei)
+                    {
+                        allValues[faceStart++] = pf[facei];
+                    }
                 }
             }
 
-            mapper_.distribute(allValues);
+            distribute(fieldName_, allValues);
             newValues.transfer(allValues);
 
             break;
@@ -322,6 +647,197 @@ Foam::mappedPatchFieldBase<Type>::mappedField() const
 }
 
 
+//template<class Type>
+//Foam::tmp<Foam::Field<Type>>
+//Foam::mappedPatchFieldBase<Type>::mappedField() const
+//{
+//    const GeometricField<Type, fvPatchField, volMesh>& fld = sampleField();
+//    return mappedField<Type>(fld);
+//}
+
+
+template<class Type>
+Foam::tmp<Foam::Field<Type>>
+Foam::mappedPatchFieldBase<Type>::mappedInternalField() const
+{
+    // Swap to obtain full local values of neighbour internal field
+    tmp<Field<Type>> tnbrIntFld(new Field<Type>());
+    Field<Type>& nbrIntFld = tnbrIntFld.ref();
+
+    if (mapper_.sameWorld())
+    {
+        // Same world so lookup
+        const label nbrPatchID = mapper_.samplePolyPatch().index();
+        const auto& nbrField = this->sampleField();
+        nbrIntFld = nbrField.boundaryField()[nbrPatchID].patchInternalField();
+    }
+    else
+    {
+        // Different world so use my region,patch. Distribution below will
+        // do the reordering
+        nbrIntFld = patchField_.patchInternalField();
+    }
+
+    // Since we're inside initEvaluate/evaluate there might be processor
+    // comms underway. Change the tag we use.
+    int oldTag = UPstream::msgType();
+    UPstream::msgType() = oldTag+1;
+
+    distribute(fieldName_, nbrIntFld);
+
+    // Restore tag
+    UPstream::msgType() = oldTag;
+
+    return tnbrIntFld;
+}
+
+
+template<class Type>
+Foam::tmp<Foam::scalarField>
+Foam::mappedPatchFieldBase<Type>::mappedWeightField() const
+{
+    // Swap to obtain full local values of neighbour internal field
+    tmp<scalarField> tnbrKDelta(new scalarField());
+    scalarField& nbrKDelta = tnbrKDelta.ref();
+
+    if (mapper_.sameWorld())
+    {
+        // Same world so lookup
+        const auto& nbrMesh = refCast<const fvMesh>(this->mapper_.sampleMesh());
+        const label nbrPatchID = mapper_.samplePolyPatch().index();
+        const auto& nbrPatch = nbrMesh.boundary()[nbrPatchID];
+        nbrKDelta = nbrPatch.deltaCoeffs();
+    }
+    else
+    {
+        // Different world so use my region,patch. Distribution below will
+        // do the reordering
+        nbrKDelta = patchField_.patch().deltaCoeffs();
+    }
+
+
+    // Since we're inside initEvaluate/evaluate there might be processor
+    // comms underway. Change the tag we use.
+    const int oldTag = UPstream::msgType();
+    UPstream::msgType() = oldTag+1;
+
+    distribute(fieldName_ + "_deltaCoeffs", nbrKDelta);
+
+    // Restore tag
+    UPstream::msgType() = oldTag;
+
+    return tnbrKDelta;
+}
+
+
+template<class Type>
+void Foam::mappedPatchFieldBase<Type>::mappedWeightField
+(
+    const word& fieldName,
+    tmp<scalarField>& thisWeights,
+    tmp<scalarField>& nbrWeights
+) const
+{
+    thisWeights = new scalarField(patchField_.patch().deltaCoeffs());
+    if (!fieldName.empty())
+    {
+        thisWeights.ref() *=
+            patchField_.patch().template lookupPatchField
+            <
+                volScalarField,
+                scalar
+            >
+            (
+                fieldName
+            ).patchInternalField();
+    }
+
+
+    // Swap to obtain full local values of neighbour internal field
+
+    if (mapper_.sameWorld())
+    {
+        // Same world so lookup
+        const auto& nbrMesh = refCast<const fvMesh>(mapper_.sampleMesh());
+        const label nbrPatchID = mapper_.samplePolyPatch().index();
+        const auto& nbrPatch = nbrMesh.boundary()[nbrPatchID];
+
+        nbrWeights = new scalarField(nbrPatch.deltaCoeffs());
+
+        if (!fieldName.empty())
+        {
+            // Weightfield is volScalarField
+            const auto& nbrWeightField =
+                nbrMesh.template lookupObject<volScalarField>(fieldName);
+            nbrWeights.ref() *=
+                nbrWeightField.boundaryField()[nbrPatchID].patchInternalField();
+        }
+    }
+    else
+    {
+        // Different world so use my region,patch. Distribution below will
+        // do the reordering
+        nbrWeights = new scalarField(thisWeights());
+    }
+
+    // Since we're inside initEvaluate/evaluate there might be processor
+    // comms underway. Change the tag we use.
+    int oldTag = UPstream::msgType();
+    UPstream::msgType() = oldTag+1;
+
+    distribute(fieldName_ + "_weights", nbrWeights.ref());
+
+    // Restore tag
+    UPstream::msgType() = oldTag;
+}
+
+
+template<class Type>
+const Foam::mappedPatchBase& Foam::mappedPatchFieldBase<Type>::mapper
+(
+    const fvPatch& p,
+    const DimensionedField<Type, volMesh>& iF
+)
+{
+    if (!isA<mappedPatchBase>(p.patch()))
+    {
+        FatalErrorInFunction
+            << "Incorrect patch type " << p.patch().type()
+            << " for patch " << p.patch().name()
+            << " of field " << iF.name()
+            << " in file " << iF.objectPath() << nl
+            << "Type should be a mappedPatch"
+            << exit(FatalError);
+    }
+    return refCast<const mappedPatchBase>(p.patch());
+}
+
+
+template<class Type>
+template<class T>
+void Foam::mappedPatchFieldBase<Type>::initRetrieveField
+(
+    const word& fieldName,
+    const Field<T>& fld
+) const
+{
+    if (mapper_.sampleDatabase())
+    {
+        // Store my data on receive buffers (reverse of storeField;
+        // i.e. retrieveField will obtain patchField)
+        initRetrieveField
+        (
+            patchField_.internalField().time(),
+            mapper_.sampleRegion(),
+            mapper_.samplePatch(),
+            mapper_.map(),
+            fieldName,
+            fld
+        );
+    }
+}
+
+
 template<class Type>
 void Foam::mappedPatchFieldBase<Type>::write(Ostream& os) const
 {
@@ -333,7 +849,10 @@ void Foam::mappedPatchFieldBase<Type>::write(Ostream& os) const
         os.writeEntry("average", average_);
     }
 
-    os.writeEntry("interpolationScheme", interpolationScheme_);
+    if (mapper_.mode() == mappedPatchBase::NEARESTCELL)
+    {
+        os.writeEntry("interpolationScheme", interpolationScheme_);
+    }
 }
 
 
diff --git a/src/finiteVolume/fields/fvPatchFields/derived/mappedField/mappedPatchFieldBase.H b/src/finiteVolume/fields/fvPatchFields/derived/mappedField/mappedPatchFieldBase.H
index 61973cba68..62c62e3da4 100644
--- a/src/finiteVolume/fields/fvPatchFields/derived/mappedField/mappedPatchFieldBase.H
+++ b/src/finiteVolume/fields/fvPatchFields/derived/mappedField/mappedPatchFieldBase.H
@@ -67,6 +67,7 @@ namespace Foam
 // Forward declarations
 class mappedPatchBase;
 template<class> class interpolation;
+class mapDistribute;
 
 /*---------------------------------------------------------------------------*\
                     Class mappedPatchFieldBase Declaration
@@ -80,6 +81,7 @@ class mappedPatchFieldBase
         //- Selective retrieval of "average" entry from the dictionary
         static Type getAverage(const dictionary& dict, bool mandatory);
 
+
 protected:
 
     // Protected data
@@ -104,6 +106,21 @@ protected:
         word interpolationScheme_;
 
 
+    // Protected Member Functions
+
+        //- Construct field from registered elements
+        template<class T>
+        void initRetrieveField
+        (
+            const objectRegistry& obr,
+            const word& region,
+            const word& patch,
+            const mapDistribute& map,
+            const word& fieldName,
+            const Field<T>& fld
+        ) const;
+
+
 public:
 
     // Constructors
@@ -127,6 +144,16 @@ public:
             const dictionary& dict
         );
 
+        //- Construct from dictionary and initial field value
+        //  (for when running in database mode)
+        mappedPatchFieldBase
+        (
+            const mappedPatchBase& mapper,
+            const fvPatchField<Type>& patchField,
+            const dictionary& dict,
+            const Field<Type>& fld
+        );
+
         //- Construct empty
         mappedPatchFieldBase
         (
@@ -135,7 +162,7 @@ public:
         );
 
         //- Construct copy
-        mappedPatchFieldBase
+        explicit mappedPatchFieldBase
         (
             const mappedPatchFieldBase<Type>& mapper
         );
@@ -155,14 +182,84 @@ public:
 
     // Member Functions
 
+        //- Field to sample. Either on my or nbr mesh
+        template<class T>
+        const GeometricField<T, fvPatchField, volMesh>& sampleField
+        (
+            const word& fieldName
+        ) const;
+
         //- Field to sample. Either on my or nbr mesh
         const GeometricField<Type, fvPatchField, volMesh>& sampleField() const;
 
         //- Map sampleField onto *this patch
         virtual tmp<Field<Type>> mappedField() const;
 
+        //- Map internal of sampleField onto *this patch
+        virtual tmp<Field<Type>> mappedInternalField() const;
+
+        //- Map optional weightField onto *this patch. Default is deltaCoeffs
+        virtual tmp<scalarField> mappedWeightField() const;
+
+        //- Map optional weightField (given by name) onto *this patch
+        virtual void mappedWeightField
+        (    
+            const word& weightFieldName,
+            tmp<scalarField>& thisWeights,
+            tmp<scalarField>& nbrWeights
+        ) const;
+
         //- Write
         virtual void write(Ostream& os) const;
+
+
+        // Helpers
+
+            //- Check that patch is of correct type
+            static const mappedPatchBase& mapper
+            (
+                const fvPatch& p,
+                const DimensionedField<Type, volMesh>& iF
+            );
+
+            //- Initialise field to retrieve (used e.g. when value read from
+            //  dictionary)
+            template<class T>
+            void initRetrieveField
+            (
+                const word& fieldName,
+                const Field<T>& fld
+            ) const;
+
+            //- Store elements of field onto (sub) registry
+            template<class T>
+            void storeField
+            (
+                const objectRegistry& obr,
+                const word& region,
+                const word& patch,
+                const labelListList& procToMap,
+                const word& fieldName,
+                const Field<T>& fld
+            ) const;
+
+            //- Construct field from registered elements
+            template<class T>
+            void retrieveField
+            (
+                const bool allowUnset,
+                const objectRegistry& obr,
+                const word& region,
+                const word& patch,
+                const labelListList& procToMap,
+                const word& fieldName,
+                Field<T>& fld
+            ) const;
+
+            //- Wrapper for mapDistribute::distribute that knows about
+            //- dabase mapping
+            template<class T>
+            void distribute(const word& fieldName, Field<T>& newValues) const;
 };
 
 
diff --git a/src/finiteVolume/fields/fvPatchFields/derived/mappedFixedValue/mappedFixedValueFvPatchField.C b/src/finiteVolume/fields/fvPatchFields/derived/mappedFixedValue/mappedFixedValueFvPatchField.C
index 8b768773ed..b3bbd452ce 100644
--- a/src/finiteVolume/fields/fvPatchFields/derived/mappedFixedValue/mappedFixedValueFvPatchField.C
+++ b/src/finiteVolume/fields/fvPatchFields/derived/mappedFixedValue/mappedFixedValueFvPatchField.C
@@ -38,7 +38,7 @@ Foam::mappedFixedValueFvPatchField<Type>::mappedFixedValueFvPatchField
 )
 :
     fixedValueFvPatchField<Type>(p, iF),
-    mappedPatchFieldBase<Type>(this->mapper(p, iF), *this)
+    mappedPatchFieldBase<Type>(mappedPatchFieldBase<Type>::mapper(p, iF), *this)
 {}
 
 
@@ -51,7 +51,13 @@ Foam::mappedFixedValueFvPatchField<Type>::mappedFixedValueFvPatchField
 )
 :
     fixedValueFvPatchField<Type>(p, iF, dict),
-    mappedPatchFieldBase<Type>(this->mapper(p, iF), *this, dict)
+    mappedPatchFieldBase<Type>
+    (
+        mappedPatchFieldBase<Type>::mapper(p, iF),
+        *this,
+        dict,
+        *this   // initial value for database operation
+    )
 {}
 
 
@@ -65,7 +71,12 @@ Foam::mappedFixedValueFvPatchField<Type>::mappedFixedValueFvPatchField
 )
 :
     fixedValueFvPatchField<Type>(ptf, p, iF, mapper),
-    mappedPatchFieldBase<Type>(this->mapper(p, iF), *this, ptf)
+    mappedPatchFieldBase<Type>
+    (
+        mappedPatchFieldBase<Type>::mapper(p, iF),
+        *this,
+        ptf
+    )
 {}
 
 
@@ -88,32 +99,17 @@ Foam::mappedFixedValueFvPatchField<Type>::mappedFixedValueFvPatchField
 )
 :
     fixedValueFvPatchField<Type>(ptf, iF),
-    mappedPatchFieldBase<Type>(this->mapper(this->patch(), iF), *this, ptf)
+    mappedPatchFieldBase<Type>
+    (
+        mappedPatchFieldBase<Type>::mapper(this->patch(), iF),
+        *this,
+        ptf
+    )
 {}
 
 
 // * * * * * * * * * * * * * * * Member Functions  * * * * * * * * * * * * * //
 
-template<class Type>
-const Foam::mappedPatchBase& Foam::mappedFixedValueFvPatchField<Type>::mapper
-(
-    const fvPatch& p,
-    const DimensionedField<Type, volMesh>& iF
-)
-{
-    if (!isA<mappedPatchBase>(p.patch()))
-    {
-        FatalErrorInFunction
-            << "' not type '" << mappedPatchBase::typeName << "'"
-            << "\n    for patch " << p.patch().name()
-            << " of field " << iF.name()
-            << " in file " << iF.objectPath()
-            << exit(FatalError);
-    }
-    return refCast<const mappedPatchBase>(p.patch());
-}
-
-
 template<class Type>
 void Foam::mappedFixedValueFvPatchField<Type>::updateCoeffs()
 {
diff --git a/src/finiteVolume/fields/fvPatchFields/derived/mappedFixedValue/mappedFixedValueFvPatchField.H b/src/finiteVolume/fields/fvPatchFields/derived/mappedFixedValue/mappedFixedValueFvPatchField.H
index 827212231d..fdf0ce6f7b 100644
--- a/src/finiteVolume/fields/fvPatchFields/derived/mappedFixedValue/mappedFixedValueFvPatchField.H
+++ b/src/finiteVolume/fields/fvPatchFields/derived/mappedFixedValue/mappedFixedValueFvPatchField.H
@@ -103,18 +103,6 @@ class mappedFixedValueFvPatchField
     public fixedValueFvPatchField<Type>,
     public mappedPatchFieldBase<Type>
 {
-
-protected:
-
-    // Protected Member Functions
-
-        const mappedPatchBase& mapper
-        (
-            const fvPatch& p,
-            const DimensionedField<Type, volMesh>& iF
-        );
-
-
 public:
 
     //- Runtime type information
@@ -190,6 +178,7 @@ public:
             //- Update the coefficients associated with the patch field
             virtual void updateCoeffs();
 
+
         //- Write
         virtual void write(Ostream&) const;
 };
diff --git a/src/finiteVolume/fields/fvPatchFields/derived/mappedMixed/mappedMixedFvPatchField.C b/src/finiteVolume/fields/fvPatchFields/derived/mappedMixed/mappedMixedFvPatchField.C
new file mode 100644
index 0000000000..d05fc6f33d
--- /dev/null
+++ b/src/finiteVolume/fields/fvPatchFields/derived/mappedMixed/mappedMixedFvPatchField.C
@@ -0,0 +1,242 @@
+/*---------------------------------------------------------------------------*\
+  =========                 |
+  \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
+   \\    /   O peration     |
+    \\  /    A nd           | www.openfoam.com
+     \\/     M anipulation  |
+-------------------------------------------------------------------------------
+    Copyright (C) 2020 OpenCFD Ltd.
+-------------------------------------------------------------------------------
+License
+    This file is part of OpenFOAM.
+
+    OpenFOAM is free software: you can redistribute it and/or modify it
+    under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    OpenFOAM is distributed in the hope that it will be useful, but WITHOUT
+    ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+    FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+    for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with OpenFOAM.  If not, see <http://www.gnu.org/licenses/>.
+
+\*---------------------------------------------------------------------------*/
+
+#include "mappedMixedFvPatchField.H"
+#include "volFields.H"
+#include "interpolationCell.H"
+#include "mappedFixedValueFvPatchField.H"
+
+// * * * * * * * * * * * * * * * * Constructors  * * * * * * * * * * * * * * //
+
+template<class Type>
+Foam::mappedMixedFvPatchField<Type>::mappedMixedFvPatchField
+(
+    const fvPatch& p,
+    const DimensionedField<Type, volMesh>& iF
+)
+:
+    mixedFvPatchField<Type>(p, iF),
+    mappedPatchFieldBase<Type>
+    (
+        mappedFixedValueFvPatchField<Type>::mapper(p, iF),
+        *this
+    ),
+    weightFieldName_(word::null)
+{
+    this->refValue() = Zero;
+    this->refGrad() = Zero;
+    this->valueFraction() = 0.0;
+}
+
+
+template<class Type>
+Foam::mappedMixedFvPatchField<Type>::mappedMixedFvPatchField
+(
+    const fvPatch& p,
+    const DimensionedField<Type, volMesh>& iF,
+    const dictionary& dict
+)
+:
+    mixedFvPatchField<Type>(p, iF, dict),
+    mappedPatchFieldBase<Type>
+    (
+        mappedFixedValueFvPatchField<Type>::mapper(p, iF),
+        *this,
+        dict
+    ),
+    weightFieldName_(dict.getOrDefault<word>("weightField", word::null))
+{
+    mixedFvPatchField<Type>::operator=
+    (
+        Field<Type>("value", dict, p.size())
+    );
+
+    if (dict.found("refValue"))
+    {
+        // Full restart
+        this->refValue() = Field<Type>("refValue", dict, p.size());
+        this->refGrad() = Field<Type>("refGradient", dict, p.size());
+        this->valueFraction() = scalarField("valueFraction", dict, p.size());
+    }
+    else
+    {
+        // Start from user entered data. Assume fixedValue.
+        this->refValue() = *this;
+        this->refGrad() = Zero;
+        this->valueFraction() = 1.0;
+    }
+
+    // Store patch value as initial guess when running in database mode
+    mappedPatchFieldBase<Type>::initRetrieveField
+    (
+        this->internalField().name(),
+        *this
+    );
+    mappedPatchFieldBase<Type>::initRetrieveField
+    (
+        this->internalField().name() + "_weights",
+        this->patch().deltaCoeffs()
+    );
+}
+
+
+template<class Type>
+Foam::mappedMixedFvPatchField<Type>::mappedMixedFvPatchField
+(
+    const mappedMixedFvPatchField<Type>& ptf,
+    const fvPatch& p,
+    const DimensionedField<Type, volMesh>& iF,
+    const fvPatchFieldMapper& mapper
+)
+:
+    mixedFvPatchField<Type>(ptf, p, iF, mapper),
+    mappedPatchFieldBase<Type>
+    (
+        mappedFixedValueFvPatchField<Type>::mapper(p, iF),
+        *this,
+        ptf
+    ),
+    weightFieldName_(ptf.weightFieldName_)
+{}
+
+
+template<class Type>
+Foam::mappedMixedFvPatchField<Type>::mappedMixedFvPatchField
+(
+    const mappedMixedFvPatchField<Type>& ptf
+)
+:
+    mixedFvPatchField<Type>(ptf),
+    mappedPatchFieldBase<Type>(ptf),
+    weightFieldName_(ptf.weightFieldName_)
+{}
+
+
+template<class Type>
+Foam::mappedMixedFvPatchField<Type>::mappedMixedFvPatchField
+(
+    const mappedMixedFvPatchField<Type>& ptf,
+    const DimensionedField<Type, volMesh>& iF
+)
+:
+    mixedFvPatchField<Type>(ptf, iF),
+    mappedPatchFieldBase<Type>
+    (
+        mappedFixedValueFvPatchField<Type>::mapper(ptf.patch(), iF),
+        *this,
+        ptf
+    ),
+    weightFieldName_(ptf.weightFieldName_)
+{}
+
+
+// * * * * * * * * * * * * * * * Member Functions  * * * * * * * * * * * * * //
+
+template<class Type>
+void Foam::mappedMixedFvPatchField<Type>::autoMap(const fvPatchFieldMapper& m)
+{
+    mixedFvPatchField<Type>::autoMap(m);
+}
+
+
+template<class Type>
+void Foam::mappedMixedFvPatchField<Type>::rmap
+(
+    const fvPatchField<Type>& ptf,
+    const labelList& addr
+)
+{
+    mixedFvPatchField<Type>::rmap(ptf, addr);
+}
+
+
+template<class Type>
+void Foam::mappedMixedFvPatchField<Type>::updateCoeffs()
+{
+    if (this->updated())
+    {
+        return;
+    }
+
+    const tmp<Field<Type>> nbrIntFld(this->mappedInternalField());
+
+    //- Unweighted
+    //const tmp<scalarField> nbrKDelta(this->mappedWeightField());
+
+    //- Weighted
+    tmp<scalarField> myKDelta;
+    tmp<scalarField> nbrKDelta;
+    this->mappedWeightField(weightFieldName_, myKDelta, nbrKDelta);
+
+    // Both sides agree on
+    // - temperature : (myKDelta*fld + nbrKDelta*nbrFld)/(myKDelta+nbrKDelta)
+    // - gradient    : (temperature-fld)*delta
+    // We've got a degree of freedom in how to implement this in a mixed bc.
+    // (what gradient, what fixedValue and mixing coefficient)
+    // Two reasonable choices:
+    // 1. specify above temperature on one side (preferentially the high side)
+    //    and above gradient on the other. So this will switch between pure
+    //    fixedvalue and pure fixedgradient
+    // 2. specify gradient and temperature such that the equations are the
+    //    same on both sides. This leads to the choice of
+    //    - refGradient = zero gradient
+    //    - refValue = neighbour value
+    //    - mixFraction = nbrKDelta / (nbrKDelta + myKDelta())
+
+    this->refValue() = nbrIntFld;
+    this->refGrad() = Zero;
+    this->valueFraction() = nbrKDelta()/(nbrKDelta() + myKDelta());
+
+    mixedFvPatchField<Type>::updateCoeffs();
+
+    if (debug)
+    {
+        Info<< this->patch().boundaryMesh().mesh().name() << ':'
+            << this->patch().name() << ':'
+            << this->internalField().name() << " <- "
+            << this->mapper_.sampleRegion() << ':'
+            << this->mapper_.samplePatch() << ':'
+            << this->fieldName_ << " :"
+            << " value "
+            << " min:" << gMin(*this)
+            << " max:" << gMax(*this)
+            << " avg:" << gAverage(*this)
+            << endl;
+    }
+}
+
+
+template<class Type>
+void Foam::mappedMixedFvPatchField<Type>::write(Ostream& os) const
+{
+    mappedPatchFieldBase<Type>::write(os);
+    os.writeEntryIfDifferent<word>("weightField", word::null, weightFieldName_);
+    mixedFvPatchField<Type>::write(os);
+}
+
+
+// ************************************************************************* //
diff --git a/src/finiteVolume/fields/fvPatchFields/derived/mappedMixed/mappedMixedFvPatchField.H b/src/finiteVolume/fields/fvPatchFields/derived/mappedMixed/mappedMixedFvPatchField.H
new file mode 100644
index 0000000000..3da0a9e034
--- /dev/null
+++ b/src/finiteVolume/fields/fvPatchFields/derived/mappedMixed/mappedMixedFvPatchField.H
@@ -0,0 +1,232 @@
+/*---------------------------------------------------------------------------*\
+  =========                 |
+  \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
+   \\    /   O peration     |
+    \\  /    A nd           | www.openfoam.com
+     \\/     M anipulation  |
+-------------------------------------------------------------------------------
+    Copyright (C) 2019-2020 OpenCFD Ltd.
+-------------------------------------------------------------------------------
+License
+    This file is part of OpenFOAM.
+
+    OpenFOAM is free software: you can redistribute it and/or modify it
+    under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    OpenFOAM is distributed in the hope that it will be useful, but WITHOUT
+    ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+    FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+    for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with OpenFOAM.  If not, see <http://www.gnu.org/licenses/>.
+
+Class
+    Foam::mappedMixedFvPatchField
+
+Group
+    grpGenericBoundaryConditions grpCoupledBoundaryConditions
+
+Description
+    This boundary condition maps the value at a set of cells or patch faces
+    back to *this.
+
+    The sample mode is set by the underlying mapping engine, provided by the
+    mappedPatchBase class.
+
+Usage
+    \table
+        Property     | Description                      | Required | Default
+        field        | Name of field to be mapped       | no  | this field name
+        weightField  | Name of field to use as weight   | no |
+        setAverage   | Use average value                | no  | false |
+        average      | Average value to use if \c setAverage = yes | partly |
+    \endtable
+
+    Example of the boundary condition specification:
+    \verbatim
+    <patchName>
+    {
+        type            mappedMixed;
+        field           T;              // optional field name
+
+        value           uniform 273.0;
+
+        refValue        $value;
+        refGradient     uniform 0.0;
+        valueFraction   uniform 1.0;
+    }
+    \endverbatim
+
+Note
+    Supports multi-world operation:
+
+    +----+                      +----+
+    |    |                      |    |
+    |    |                      |    |
+    +----+                      +----+
+    worldA                      worldB
+    regionA                     regionB
+    patchA                      patchB
+
+
+See also
+    Foam::mappedPatchBase
+    Foam::mappedPolyPatch
+    Foam::mappedFvPatch
+    Foam::mappedFieldFvPatchField
+    Foam::mixedFvPatchField
+
+SourceFiles
+    mappedMixedFvPatchField.C
+
+\*---------------------------------------------------------------------------*/
+
+#ifndef mappedMixedFvPatchField_H
+#define mappedMixedFvPatchField_H
+
+#include "mappedPatchFieldBase.H"
+#include "mixedFvPatchFields.H"
+
+// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
+
+namespace Foam
+{
+
+/*---------------------------------------------------------------------------*\
+                  Class mappedMixedFvPatchField Declaration
+\*---------------------------------------------------------------------------*/
+
+template<class Type>
+class mappedMixedFvPatchField
+:
+    public mixedFvPatchField<Type>,
+    public mappedPatchFieldBase<Type>
+{
+
+        //- Name of weight field to sample
+        word weightFieldName_;
+
+
+public:
+
+    //- Runtime type information
+    TypeName("mappedMixed");
+
+
+    // Constructors
+
+        //- Construct from patch and internal field
+        mappedMixedFvPatchField
+        (
+            const fvPatch&,
+            const DimensionedField<Type, volMesh>&
+        );
+
+        //- Construct from patch, internal field and dictionary
+        mappedMixedFvPatchField
+        (
+            const fvPatch&,
+            const DimensionedField<Type, volMesh>&,
+            const dictionary&
+        );
+
+        //- Construct by mapping given
+        //  mappedMixedFvPatchField
+        //  onto a new patch
+        mappedMixedFvPatchField
+        (
+            const mappedMixedFvPatchField<Type>&,
+            const fvPatch&,
+            const DimensionedField<Type, volMesh>&,
+            const fvPatchFieldMapper&
+        );
+
+        //- Construct as copy
+        mappedMixedFvPatchField
+        (
+            const mappedMixedFvPatchField<Type>&
+        );
+
+        //- Construct and return a clone
+        virtual tmp<fvPatchField<Type>> clone() const
+        {
+            return tmp<fvPatchField<Type>>
+            (
+                new mappedMixedFvPatchField<Type>
+                (
+                    *this
+                )
+            );
+        }
+
+        //- Construct as copy setting internal field reference
+        mappedMixedFvPatchField
+        (
+            const mappedMixedFvPatchField<Type>&,
+            const DimensionedField<Type, volMesh>&
+        );
+
+        //- Construct and return a clone setting internal field reference
+        virtual tmp<fvPatchField<Type>> clone
+        (
+            const DimensionedField<Type, volMesh>& iF
+        ) const
+        {
+            return tmp<fvPatchField<Type>>
+            (
+                new mappedMixedFvPatchField<Type>
+                (
+                    *this,
+                    iF
+                )
+            );
+        }
+
+
+    // Member functions
+
+        // Mapping functions
+
+            //- Map (and resize as needed) from self given a mapping object
+            virtual void autoMap
+            (
+                const fvPatchFieldMapper&
+            );
+
+            //- Reverse map the given fvPatchField onto this fvPatchField
+            virtual void rmap
+            (
+                const fvPatchField<Type>&,
+                const labelList&
+            );
+
+
+        // Evaluation functions
+
+            //- Update the coefficients associated with the patch field
+            virtual void updateCoeffs();
+
+
+        //- Write
+        virtual void write(Ostream&) const;
+};
+
+
+// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
+
+} // End namespace Foam
+
+// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
+
+#ifdef NoRepository
+    #include "mappedMixedFvPatchField.C"
+#endif
+
+// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
+
+#endif
+
+// ************************************************************************* //
diff --git a/src/finiteVolume/fields/fvPatchFields/derived/mappedMixed/mappedMixedFvPatchFields.C b/src/finiteVolume/fields/fvPatchFields/derived/mappedMixed/mappedMixedFvPatchFields.C
new file mode 100644
index 0000000000..609f37bf4d
--- /dev/null
+++ b/src/finiteVolume/fields/fvPatchFields/derived/mappedMixed/mappedMixedFvPatchFields.C
@@ -0,0 +1,44 @@
+/*---------------------------------------------------------------------------*\
+  =========                 |
+  \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
+   \\    /   O peration     |
+    \\  /    A nd           | Copyright (C) 2020 OpenCFD Ltd.
+     \\/     M anipulation  |
+-------------------------------------------------------------------------------
+License
+    This file is part of OpenFOAM.
+
+    OpenFOAM is free software: you can redistribute it and/or modify it
+    under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    OpenFOAM is distributed in the hope that it will be useful, but WITHOUT
+    ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+    FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+    for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with OpenFOAM.  If not, see <http://www.gnu.org/licenses/>.
+
+\*---------------------------------------------------------------------------*/
+
+#include "mappedMixedFvPatchFields.H"
+#include "volMesh.H"
+#include "addToRunTimeSelectionTable.H"
+
+// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
+
+namespace Foam
+{
+
+// * * * * * * * * * * * * * * Static Data Members * * * * * * * * * * * * * //
+
+//makeTemplatePatchTypeField(scalar, mappedMixed);
+makePatchFields(mappedMixed);
+
+// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
+
+} // End namespace Foam
+
+// ************************************************************************* //
diff --git a/src/finiteVolume/fields/fvPatchFields/derived/mappedMixed/mappedMixedFvPatchFields.H b/src/finiteVolume/fields/fvPatchFields/derived/mappedMixed/mappedMixedFvPatchFields.H
new file mode 100644
index 0000000000..2f7de22809
--- /dev/null
+++ b/src/finiteVolume/fields/fvPatchFields/derived/mappedMixed/mappedMixedFvPatchFields.H
@@ -0,0 +1,51 @@
+/*---------------------------------------------------------------------------*\
+  =========                 |
+  \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
+   \\    /   O peration     |
+    \\  /    A nd           | Copyright (C) 2019 OpenCFD Ltd.
+     \\/     M anipulation  |
+-------------------------------------------------------------------------------
+License
+    This file is part of OpenFOAM.
+
+    OpenFOAM is free software: you can redistribute it and/or modify it
+    under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    OpenFOAM is distributed in the hope that it will be useful, but WITHOUT
+    ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+    FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+    for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with OpenFOAM.  If not, see <http://www.gnu.org/licenses/>.
+
+\*---------------------------------------------------------------------------*/
+
+#ifndef mappedMixedFvPatchFields_H
+#define mappedMixedFvPatchFields_H
+
+#include "mappedMixedFvPatchField.H"
+#include "fieldTypes.H"
+#include "fvPatchFields.H"
+
+// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
+
+namespace Foam
+{
+
+// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
+
+//makePatchTypeFieldTypedef(scalar, mappedMixed);
+makePatchTypeFieldTypedefs(mappedMixed)
+
+// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
+
+} // End namespace Foam
+
+// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
+
+#endif
+
+// ************************************************************************* //
diff --git a/src/functionObjects/utilities/Make/files b/src/functionObjects/utilities/Make/files
index c3f384ee69..e9bb23307d 100644
--- a/src/functionObjects/utilities/Make/files
+++ b/src/functionObjects/utilities/Make/files
@@ -39,4 +39,6 @@ writeObjects/writeObjects.C
 
 thermoCoupleProbes/thermoCoupleProbes.C
 
+syncObjects/syncObjects.C
+
 LIB = $(FOAM_LIBBIN)/libutilityFunctionObjects
diff --git a/src/functionObjects/utilities/syncObjects/syncObjects.C b/src/functionObjects/utilities/syncObjects/syncObjects.C
new file mode 100644
index 0000000000..694eecfc92
--- /dev/null
+++ b/src/functionObjects/utilities/syncObjects/syncObjects.C
@@ -0,0 +1,228 @@
+/*---------------------------------------------------------------------------*\
+  =========                 |
+  \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
+   \\    /   O peration     |
+    \\  /    A nd           | www.openfoam.com
+     \\/     M anipulation  |
+-------------------------------------------------------------------------------
+    Copyright (C) 2020 OpenCFD Ltd.
+-------------------------------------------------------------------------------
+License
+    This file is part of OpenFOAM.
+
+    OpenFOAM is free software: you can redistribute it and/or modify it
+    under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    OpenFOAM is distributed in the hope that it will be useful, but WITHOUT
+    ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+    FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+    for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with OpenFOAM.  If not, see <http://www.gnu.org/licenses/>.
+
+\*---------------------------------------------------------------------------*/
+
+#include "syncObjects.H"
+#include "Time.H"
+#include "polyMesh.H"
+#include "addToRunTimeSelectionTable.H"
+#include "objectRegistry.H"
+#include "mappedPatchBase.H"
+
+// * * * * * * * * * * * * * * Static Data Members * * * * * * * * * * * * * //
+
+namespace Foam
+{
+namespace functionObjects
+{
+    defineTypeNameAndDebug(syncObjects, 0);
+
+    addToRunTimeSelectionTable
+    (
+        functionObject,
+        syncObjects,
+        dictionary
+    );
+}
+}
+
+
+// * * * * * * * * * * * * * Private Member Functions  * * * * * * * * * * * //
+
+
+// * * * * * * * * * * * * * * * * Constructors  * * * * * * * * * * * * * * //
+
+Foam::functionObjects::syncObjects::syncObjects
+(
+    const word& name,
+    const Time& runTime,
+    const dictionary& dict
+)
+:
+    functionObject(name),
+    obr_
+    (
+        //runTime.lookupObject<objectRegistry>
+        //(
+        //    dict.lookupOrDefault("region", polyMesh::defaultRegion)
+        //)
+        runTime
+    )
+{
+    read(dict);
+}
+
+
+// * * * * * * * * * * * * * * * Member Functions  * * * * * * * * * * * * * //
+
+void Foam::functionObjects::syncObjects::sync()
+{
+    if (debug)
+    {
+        Pout<< type() << " : sync()"
+            << " root:" << root_ << endl;
+    }
+
+    const label oldWarnComm = UPstream::warnComm;
+    UPstream::warnComm = 0;
+
+    if (!Pstream::parRun())
+    {
+        return;
+    }
+
+
+    // Send my data to all other processors
+    // ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+    // Note provision of explicit all-world communicator
+    PstreamBuffers pBufs
+    (
+        Pstream::commsTypes::nonBlocking,
+        UPstream::msgType(),
+        0
+    );
+
+
+    const label nProcs = Pstream::nProcs(pBufs.comm());
+    for (label proci = 0; proci < nProcs; proci++)
+    {
+        // Get database to send
+        const objectRegistry& sendObr = mappedPatchBase::subRegistry
+        (
+            obr_,
+            mappedPatchBase::sendPath(root_, proci)
+        );
+
+        // Pack into dictionary
+        dictionary sendDataDict;
+        mappedPatchBase::writeDict(sendObr, sendDataDict);
+
+        //Pout<< "** to processor " << proci
+        //    << " sendObr:" << sendObr.objectPath()
+        //    << " sending dictionary:" << sendDataDict << endl;
+        UOPstream os(proci, pBufs);
+        os << sendDataDict;
+    }
+
+    // Start sending and receiving and block
+    pBufs.finishedSends();
+
+    for (label proci = 0; proci < nProcs; proci++)
+    {
+        // Get database to receive data into
+        const objectRegistry& receiveObr = mappedPatchBase::subRegistry
+        (
+            obr_,
+            mappedPatchBase::receivePath(root_, proci)
+        );
+        //Pout<< "** from processor " << proci
+        //        << " receiveObr:" << receiveObr.objectPath()
+        //    << " receiving dictionary" << endl;
+        UIPstream is(proci, pBufs);
+        const dictionary fromProcDict(is);
+        //Pout<< "** from processor " << proci
+        //    << " received dictionary:" << fromProcDict << endl;
+
+        mappedPatchBase::readDict
+        (
+            fromProcDict,
+            const_cast<objectRegistry&>(receiveObr)
+        );
+    }
+
+    //if (debug)
+    //{
+    //    dictionary allDict;
+    //    // Add send subdictionary
+    //    dictionary& sendDict = allDict.subDictOrAdd("send");
+    //    mappedPatchBase::writeDict
+    //    (
+    //        mappedPatchBase::subRegistry(obr_, "send"),
+    //        sendDict
+    //    );
+    //    // Add receive subdictionary
+    //    dictionary& receiveDict = allDict.subDictOrAdd("receive");
+    //    mappedPatchBase::writeDict
+    //    (
+    //        mappedPatchBase::subRegistry(obr_, "receive"),
+    //        receiveDict
+    //    );
+    //    Pout<< type() << " : after synchronisation:" << allDict << endl;
+    //}
+
+    UPstream::warnComm = oldWarnComm;
+}
+
+
+bool Foam::functionObjects::syncObjects::read(const dictionary& dict)
+{
+    if (debug)
+    {
+        Pout<< type() << " : read(const dictionary&)" << endl;
+    }
+
+    functionObject::read(dict);
+    root_ = dict.getOrDefault<fileName>("root", fileName::null);
+
+    if (debug)
+    {
+        Pout<< type() << " : root:" << root_ << endl;
+    }
+
+    // Make sure that at startup we're doing a sync (execute below only gets
+    // called at end of timeloop)
+    sync();
+
+    return true;
+}
+
+
+bool Foam::functionObjects::syncObjects::execute()
+{
+    if (debug)
+    {
+        Pout<< type() << " : execute()" << endl;
+    }
+
+    sync();
+
+    return true;
+}
+
+
+bool Foam::functionObjects::syncObjects::write()
+{
+    if (debug)
+    {
+        Pout<< type() << " : write()" << endl;
+    }
+
+    return true;
+}
+
+
+// ************************************************************************* //
diff --git a/src/functionObjects/utilities/syncObjects/syncObjects.H b/src/functionObjects/utilities/syncObjects/syncObjects.H
new file mode 100644
index 0000000000..8b6c135e31
--- /dev/null
+++ b/src/functionObjects/utilities/syncObjects/syncObjects.H
@@ -0,0 +1,178 @@
+/*---------------------------------------------------------------------------*\
+  =========                 |
+  \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
+   \\    /   O peration     |
+    \\  /    A nd           | www.openfoam.com
+     \\/     M anipulation  |
+-------------------------------------------------------------------------------
+    Copyright (C) 2020 OpenCFD Ltd.
+-------------------------------------------------------------------------------
+License
+    This file is part of OpenFOAM.
+
+    OpenFOAM is free software: you can redistribute it and/or modify it
+    under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    OpenFOAM is distributed in the hope that it will be useful, but WITHOUT
+    ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+    FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+    for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with OpenFOAM.  If not, see <http://www.gnu.org/licenses/>.
+
+Class
+    Foam::functionObjects::syncObjects
+
+Group
+    grpUtilitiesFunctionObjects
+
+Description
+    Copies content of local objectRegistry to all processors.
+
+    Currently only supports IOFields. It is used to distribute IOFields
+    from different processors/regions/worlds
+    when doing loose coupling. To be used in combination with 'mapped'
+    boundary conditions.
+
+Usage
+    Example of function object specification:
+    \verbatim
+    syncObjects1
+    {
+        type        syncObjects;
+        libs        ("libutilityFunctionObjects.so");
+        ...
+
+        // Where is data located relative to runTime. Given as a filename
+        // with every '/' indicating a sub-objectRegistry w.r.t. runTime.
+        // Local data is under <root>/send/processorXXX. After execution
+        // (potentially remote) data will be under the corresponding
+        // <root>/receive/processorYYY objectRegistry.
+        //root        "level0/level1/level2";
+    }
+    \endverbatim
+
+    Where the entries comprise:
+    \table
+        Property     | Description             | Required     | Default value
+        type         | type name: syncObjects  | yes          |
+        root         | relative location of data  | no          | ""
+    \endtable
+
+See also
+    Foam::functionObject
+
+SourceFiles
+    syncObjects.C
+
+\*---------------------------------------------------------------------------*/
+
+#ifndef functionObjects_syncObjects_H
+#define functionObjects_syncObjects_H
+
+#include "token.H"
+#include "functionObject.H"
+#include "IOField.H"
+
+// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
+
+namespace Foam
+{
+
+// Forward declaration of classes
+class objectRegistry;
+
+namespace functionObjects
+{
+
+/*---------------------------------------------------------------------------*\
+                Class functionObjects::syncObjects Declaration
+\*---------------------------------------------------------------------------*/
+
+class syncObjects
+:
+    public functionObject
+{
+private:
+
+    // Private data
+
+        //- Top-level registry
+        const objectRegistry& obr_;
+
+        //- objectRegistry location relative to top-level
+        fileName root_;
+
+
+    // Private Member Functions
+
+        //- No copy construct
+        syncObjects(const syncObjects&) = delete;
+
+        //- No copy assignment
+        void operator=(const syncObjects&) = delete;
+
+
+protected:
+
+        //- Do all: synchronise all IOFields and objectRegistry
+        void sync();
+
+
+public:
+
+    //- Runtime type information
+    TypeName("syncObjects");
+
+
+    // Constructors
+
+        //- Construct from Time and dictionary
+        syncObjects
+        (
+            const word& name,
+            const Time& runTime,
+            const dictionary& dict
+        );
+
+
+    //- Destructor
+    virtual ~syncObjects() = default;
+
+
+    // Member Functions
+
+        const objectRegistry& obr() const
+        {
+            return obr_;
+        }
+
+        const fileName& root() const
+        {
+            return root_;
+        }
+
+        //- Read the syncObjects data
+        virtual bool read(const dictionary&);
+
+        //- Do nothing
+        virtual bool execute();
+
+        //- Write the registered objects
+        virtual bool write();
+};
+
+
+// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
+
+} // End namespace functionObjects
+} // End namespace Foam
+
+// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
+
+#endif
+
+// ************************************************************************* //
diff --git a/src/functionObjects/utilities/syncObjects/syncObjectsTemplates.C b/src/functionObjects/utilities/syncObjects/syncObjectsTemplates.C
new file mode 100644
index 0000000000..05dc827a17
--- /dev/null
+++ b/src/functionObjects/utilities/syncObjects/syncObjectsTemplates.C
@@ -0,0 +1,33 @@
+/*---------------------------------------------------------------------------*\
+  =========                 |
+  \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
+   \\    /   O peration     |
+    \\  /    A nd           | www.openfoam.com
+     \\/     M anipulation  |
+-------------------------------------------------------------------------------
+    Copyright (C) 2020 OpenCFD Ltd.
+-------------------------------------------------------------------------------
+License
+    This file is part of OpenFOAM.
+
+    OpenFOAM is free software: you can redistribute it and/or modify it
+    under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    OpenFOAM is distributed in the hope that it will be useful, but WITHOUT
+    ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+    FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+    for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with OpenFOAM.  If not, see <http://www.gnu.org/licenses/>.
+
+\*---------------------------------------------------------------------------*/
+
+#include "objectRegistry.H"
+
+// * * * * * * * * * * * * * Private Member Functions  * * * * * * * * * * * //
+
+
+// ************************************************************************* //
diff --git a/src/meshTools/AMIInterpolation/AMIInterpolation/faceAreaWeightAMI/faceAreaWeightAMI.C b/src/meshTools/AMIInterpolation/AMIInterpolation/faceAreaWeightAMI/faceAreaWeightAMI.C
index 2be76626bd..e6fbbb1816 100644
--- a/src/meshTools/AMIInterpolation/AMIInterpolation/faceAreaWeightAMI/faceAreaWeightAMI.C
+++ b/src/meshTools/AMIInterpolation/AMIInterpolation/faceAreaWeightAMI/faceAreaWeightAMI.C
@@ -737,9 +737,9 @@ bool Foam::faceAreaWeightAMI::calculate
             extendedTgtMapPtr_->subMap(),
             false,                      // has flip
             tgtAddress_,
+            labelList(),
             ListOps::appendEqOp<label>(),
-            flipOp(),                   // flip operation
-            labelList()
+            flipOp()                    // flip operation
         );
 
         mapDistributeBase::distribute
@@ -752,9 +752,9 @@ bool Foam::faceAreaWeightAMI::calculate
             extendedTgtMapPtr_->subMap(),
             false,
             tgtWeights_,
+            scalarList(),
             ListOps::appendEqOp<scalar>(),
-            flipOp(),
-            scalarList()
+            flipOp()
         );
 
         // Note: using patch face areas calculated by the AMI method
diff --git a/src/meshTools/AMIInterpolation/AMIInterpolation/nearestFaceAMI/nearestFaceAMI.C b/src/meshTools/AMIInterpolation/AMIInterpolation/nearestFaceAMI/nearestFaceAMI.C
index 9108ddbca8..aaebecbc95 100644
--- a/src/meshTools/AMIInterpolation/AMIInterpolation/nearestFaceAMI/nearestFaceAMI.C
+++ b/src/meshTools/AMIInterpolation/AMIInterpolation/nearestFaceAMI/nearestFaceAMI.C
@@ -200,9 +200,9 @@ Foam::autoPtr<Foam::mapDistribute> Foam::nearestFaceAMI::calcDistributed
         map.subMap(),
         map.subHasFlip(),
         remoteInfo,
+        nearestZero,
         nearestEqOp(),
-        noOp(),             // no flipping
-        nearestZero
+        noOp()              // no flipping
     );
 
 
diff --git a/src/meshTools/mappedPatches/mappedPolyPatch/mappedPatchBase.C b/src/meshTools/mappedPatches/mappedPolyPatch/mappedPatchBase.C
index 329c8dac8e..48395a9738 100644
--- a/src/meshTools/mappedPatches/mappedPolyPatch/mappedPatchBase.C
+++ b/src/meshTools/mappedPatches/mappedPolyPatch/mappedPatchBase.C
@@ -46,6 +46,7 @@ License
 #include "treeDataCell.H"
 #include "DynamicField.H"
 #include "faceAreaWeightAMI.H"
+#include "OTstream.H"
 
 // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
 
@@ -84,6 +85,90 @@ Foam::mappedPatchBase::offsetModeNames_
 
 // * * * * * * * * * * * * * Private Member Functions  * * * * * * * * * * * //
 
+Foam::autoPtr<Foam::fileName> Foam::mappedPatchBase::readDatabase
+(
+    const dictionary& dict
+)
+{
+    autoPtr<fileName> dbNamePtr_;
+
+    if (dict.found("sampleDatabase"))
+    {
+        const bool useDb = dict.get<bool>("sampleDatabase");
+        if (useDb)
+        {
+            dbNamePtr_.set
+            (
+                new fileName
+                (
+                    dict.lookupOrDefault<fileName>
+                    (
+                        "sampleDatabasePath",
+                        fileName::null
+                    )
+                )
+            );
+        }
+    }
+    else if (dict.found("sampleDatabasePath"))
+    {
+        dbNamePtr_.set(new fileName(dict.get<fileName>("sampleDatabasePath")));
+    }
+
+    return dbNamePtr_;
+}
+
+
+Foam::label Foam::mappedPatchBase::communicator
+(
+    const word& sampleWorld
+)
+{
+    // Start off with local world
+    label comm = UPstream::worldComm;
+
+    if (!sampleWorld.empty() && Pstream::parRun())
+    {
+        if (!UPstream::allWorlds().found(sampleWorld))
+        {
+            FatalErrorInFunction << "Cannot find sampleWorld " << sampleWorld
+                << " in set of worlds " << UPstream::allWorlds()
+                << exit(FatalError);
+        }
+
+        const labelList& worldIDs = UPstream::worldIDs();
+
+        DynamicList<label> subRanks(worldIDs.size());
+        forAll(worldIDs, proci)
+        {
+            const label worldi = worldIDs[proci];
+            if
+            (
+                worldi == UPstream::myWorldID()
+             || UPstream::allWorlds()[worldi] == sampleWorld
+            )
+            {
+                subRanks.append(proci);
+            }
+        }
+
+        // Allocate new communicator with parent 0 (= world)
+        comm = UPstream::allocateCommunicator(0, subRanks, true);
+
+        if (debug)
+        {
+            Pout<< "mappedPatchBase::communicator :"
+                << " myWorld:" << UPstream::myWorld()
+                << " sampleWorld:" << sampleWorld
+                << " using subRanks:" << subRanks
+                << " new comm:" << comm << endl;
+        }
+    }
+
+    return comm;
+}
+
+
 Foam::tmp<Foam::pointField> Foam::mappedPatchBase::facePoints
 (
     const polyPatch& pp
@@ -114,19 +199,27 @@ Foam::tmp<Foam::pointField> Foam::mappedPatchBase::facePoints
 
 void Foam::mappedPatchBase::collectSamples
 (
+    const label mySampleWorld,      // Wanted world
     const pointField& facePoints,
-    pointField& samples,
-    labelList& patchFaceProcs,
-    labelList& patchFaces,
-    pointField& patchFc
+    pointField& samples,            // All samples
+    labelList& patchFaceWorlds,     // Per sample: wanted world
+    labelList& patchFaceProcs,      // Per sample: originating processor 
+    labelList& patchFaces,          // Per sample: originating patchFace index
+    pointField& patchFc             // Per sample: originating centre
 ) const
 {
+    const label oldComm(Pstream::warnComm);
+    Pstream::warnComm = comm_;
+
+    const label myRank = Pstream::myProcNo(comm_);
+    const label nProcs = Pstream::nProcs(comm_);
+
     // Collect all sample points and the faces they come from.
     {
-        List<pointField> globalFc(Pstream::nProcs());
-        globalFc[Pstream::myProcNo()] = facePoints;
-        Pstream::gatherList(globalFc);
-        Pstream::scatterList(globalFc);
+        List<pointField> globalFc(nProcs);
+        globalFc[myRank] = facePoints;
+        Pstream::gatherList(globalFc, Pstream::msgType(), comm_);
+        Pstream::scatterList(globalFc, Pstream::msgType(), comm_);
         // Rework into straight list
         patchFc = ListListOps::combine<pointField>
         (
@@ -136,10 +229,10 @@ void Foam::mappedPatchBase::collectSamples
     }
 
     {
-        List<pointField> globalSamples(Pstream::nProcs());
-        globalSamples[Pstream::myProcNo()] = samplePoints(facePoints);
-        Pstream::gatherList(globalSamples);
-        Pstream::scatterList(globalSamples);
+        List<pointField> globalSamples(nProcs);
+        globalSamples[myRank] = samplePoints(facePoints);
+        Pstream::gatherList(globalSamples, Pstream::msgType(), comm_);
+        Pstream::scatterList(globalSamples, Pstream::msgType(), comm_);
         // Rework into straight list
         samples = ListListOps::combine<pointField>
         (
@@ -149,11 +242,11 @@ void Foam::mappedPatchBase::collectSamples
     }
 
     {
-        labelListList globalFaces(Pstream::nProcs());
-        globalFaces[Pstream::myProcNo()] = identity(patch_.size());
+        labelListList globalFaces(nProcs);
+        globalFaces[myRank] = identity(patch_.size());
         // Distribute to all processors
-        Pstream::gatherList(globalFaces);
-        Pstream::scatterList(globalFaces);
+        Pstream::gatherList(globalFaces, Pstream::msgType(), comm_);
+        Pstream::scatterList(globalFaces, Pstream::msgType(), comm_);
 
         patchFaces = ListListOps::combine<labelList>
         (
@@ -163,11 +256,17 @@ void Foam::mappedPatchBase::collectSamples
     }
 
     {
-        labelList nPerProc(Pstream::nProcs());
-        nPerProc[Pstream::myProcNo()] = patch_.size();
-        Pstream::gatherList(nPerProc);
-        Pstream::scatterList(nPerProc);
+        labelList procToWorldIndex(nProcs);
+        procToWorldIndex[myRank] = mySampleWorld;
+        Pstream::gatherList(procToWorldIndex, Pstream::msgType(), comm_);
+        Pstream::scatterList(procToWorldIndex, Pstream::msgType(), comm_);
 
+        labelList nPerProc(nProcs);
+        nPerProc[myRank] = patch_.size();
+        Pstream::gatherList(nPerProc, Pstream::msgType(), comm_);
+        Pstream::scatterList(nPerProc, Pstream::msgType(), comm_);
+
+        patchFaceWorlds.setSize(patchFaces.size());
         patchFaceProcs.setSize(patchFaces.size());
 
         label sampleI = 0;
@@ -175,35 +274,49 @@ void Foam::mappedPatchBase::collectSamples
         {
             for (label i = 0; i < nPerProc[proci]; i++)
             {
-                patchFaceProcs[sampleI++] = proci;
+                patchFaceWorlds[sampleI] = procToWorldIndex[proci];
+                patchFaceProcs[sampleI] = proci;
+                sampleI++;
             }
         }
     }
+    Pstream::warnComm = oldComm;
 }
 
 
-// Find the processor/cell containing the samples. Does not account
-// for samples being found in two processors.
-void Foam::mappedPatchBase::findSamples
+void Foam::mappedPatchBase::findLocalSamples
 (
     const sampleMode mode,
+
+    const label mySampleWorld,  // local world to sample == my own world
+    const word& sampleRegion,   // local region to sample
+    const word& samplePatch,    // local patch to sample
+
     const pointField& samples,
-    labelList& sampleProcs,
-    labelList& sampleIndices,
-    pointField& sampleLocations
+    List<nearInfoWorld>& nearest
 ) const
 {
+    // Find the local cell containing the samples
+
+    const label myRank = Pstream::myProcNo(comm_);
+
     // Lookup the correct region
-    const polyMesh& mesh = sampleMesh();
+    const polyMesh& mesh = lookupMesh(sampleRegion);
 
     // All the info for nearest. Construct to miss
-    List<nearInfo> nearest(samples.size());
+    nearest.setSize(samples.size());
+    nearInfoWorld miss;
+    {
+        miss.first().second() = Tuple2<scalar, label>(Foam::sqr(GREAT), -1);
+        miss.second() = -1; // set world to be ignored
+    }
+    nearest = miss;
 
     switch (mode)
     {
         case NEARESTCELL:
         {
-            if (samplePatch_.size() && samplePatch_ != "none")
+            if (samplePatch.size() && samplePatch != "none")
             {
                 FatalErrorInFunction
                     << "No need to supply a patch name when in "
@@ -216,26 +329,29 @@ void Foam::mappedPatchBase::findSamples
             forAll(samples, sampleI)
             {
                 const point& sample = samples[sampleI];
+                nearInfoWorld& near = nearest[sampleI];
 
                 label celli = tree.findInside(sample);
 
                 if (celli == -1)
                 {
-                    nearest[sampleI].second().first() = Foam::sqr(GREAT);
-                    nearest[sampleI].second().second() = Pstream::myProcNo();
+                    near.first().second().first() = Foam::sqr(GREAT);
+                    near.first().second().second() = myRank;
+                    near.second() = mySampleWorld;
                 }
                 else
                 {
                     const point& cc = mesh.cellCentres()[celli];
 
-                    nearest[sampleI].first() = pointIndexHit
+                    near.first().first() = pointIndexHit
                     (
                         true,
                         cc,
                         celli
                     );
-                    nearest[sampleI].second().first() = magSqr(cc-sample);
-                    nearest[sampleI].second().second() = Pstream::myProcNo();
+                    near.first().second().first() = magSqr(cc-sample);
+                    near.first().second().second() = myRank;
+                    near.second() = mySampleWorld;
                 }
             }
             break;
@@ -243,7 +359,7 @@ void Foam::mappedPatchBase::findSamples
 
         case NEARESTONLYCELL:
         {
-            if (samplePatch_.size() && samplePatch_ != "none")
+            if (samplePatch.size() && samplePatch != "none")
             {
                 FatalErrorInFunction
                     << "No need to supply a patch name when in "
@@ -256,14 +372,16 @@ void Foam::mappedPatchBase::findSamples
             forAll(samples, sampleI)
             {
                 const point& sample = samples[sampleI];
+                nearInfoWorld& near = nearest[sampleI];
 
-                nearest[sampleI].first() = tree.findNearest(sample, sqr(GREAT));
-                nearest[sampleI].second().first() = magSqr
+                near.first().first() = tree.findNearest(sample, sqr(GREAT));
+                near.first().second().first() = magSqr
                 (
-                    nearest[sampleI].first().hitPoint()
+                    near.first().first().hitPoint()
                    -sample
                 );
-                nearest[sampleI].second().second() = Pstream::myProcNo();
+                near.first().second().second() = myRank;
+                near.second() = mySampleWorld;
             }
             break;
         }
@@ -272,14 +390,16 @@ void Foam::mappedPatchBase::findSamples
         {
             Random rndGen(123456);
 
-            const polyPatch& pp = samplePolyPatch();
+            const polyPatch& pp = lookupPatch(sampleRegion, samplePatch);
 
             if (pp.empty())
             {
                 forAll(samples, sampleI)
                 {
-                    nearest[sampleI].second().first() = Foam::sqr(GREAT);
-                    nearest[sampleI].second().second() = Pstream::myProcNo();
+                    nearInfoWorld& near = nearest[sampleI];
+                    near.first().second().first() = Foam::sqr(GREAT);
+                    near.first().second().second() = myRank;
+                    near.second() = mySampleWorld;
                 }
             }
             else
@@ -313,7 +433,8 @@ void Foam::mappedPatchBase::findSamples
                 {
                     const point& sample = samples[sampleI];
 
-                    pointIndexHit& nearInfo = nearest[sampleI].first();
+                    nearInfoWorld& near = nearest[sampleI];
+                    pointIndexHit& nearInfo = near.first().first();
                     nearInfo = boundaryTree.findNearest
                     (
                         sample,
@@ -322,17 +443,17 @@ void Foam::mappedPatchBase::findSamples
 
                     if (!nearInfo.hit())
                     {
-                        nearest[sampleI].second().first() = Foam::sqr(GREAT);
-                        nearest[sampleI].second().second() =
-                            Pstream::myProcNo();
+                        near.first().second().first() = Foam::sqr(GREAT);
+                        near.first().second().second() = myRank;
+                        near.second() = mySampleWorld;
                     }
                     else
                     {
                         point fc(pp[nearInfo.index()].centre(pp.points()));
                         nearInfo.setPoint(fc);
-                        nearest[sampleI].second().first() = magSqr(fc-sample);
-                        nearest[sampleI].second().second() =
-                            Pstream::myProcNo();
+                        near.first().second().first() = magSqr(fc-sample);
+                        near.first().second().second() = myRank;
+                        near.second() = mySampleWorld;
                     }
                 }
             }
@@ -343,14 +464,16 @@ void Foam::mappedPatchBase::findSamples
         {
             Random rndGen(123456);
 
-            const polyPatch& pp = samplePolyPatch();
+            const polyPatch& pp = lookupPatch(sampleRegion, samplePatch);
 
             if (pp.empty())
             {
                 forAll(samples, sampleI)
                 {
-                    nearest[sampleI].second().first() = Foam::sqr(GREAT);
-                    nearest[sampleI].second().second() = Pstream::myProcNo();
+                    nearInfoWorld& near = nearest[sampleI];
+                    near.first().second().first() = Foam::sqr(GREAT);
+                    near.first().second().second() = myRank;
+                    near.second() = mySampleWorld;
                 }
             }
             else
@@ -384,7 +507,8 @@ void Foam::mappedPatchBase::findSamples
                 {
                     const point& sample = samples[sampleI];
 
-                    pointIndexHit& nearInfo = nearest[sampleI].first();
+                    nearInfoWorld& near = nearest[sampleI];
+                    pointIndexHit& nearInfo = near.first().first();
                     nearInfo = boundaryTree.findNearest
                     (
                         sample,
@@ -393,17 +517,17 @@ void Foam::mappedPatchBase::findSamples
 
                     if (!nearInfo.hit())
                     {
-                        nearest[sampleI].second().first() = Foam::sqr(GREAT);
-                        nearest[sampleI].second().second() =
-                            Pstream::myProcNo();
+                        near.first().second().first() = Foam::sqr(GREAT);
+                        near.first().second().second() = myRank;
+                        near.second() = mySampleWorld;
                     }
                     else
                     {
                         const point& pt = nearInfo.hitPoint();
 
-                        nearest[sampleI].second().first() = magSqr(pt-sample);
-                        nearest[sampleI].second().second() =
-                            Pstream::myProcNo();
+                        near.first().second().first() = magSqr(pt-sample);
+                        near.first().second().second() = myRank;
+                        near.second() = mySampleWorld;
                     }
                 }
             }
@@ -412,7 +536,7 @@ void Foam::mappedPatchBase::findSamples
 
         case NEARESTFACE:
         {
-            if (samplePatch().size() && samplePatch() != "none")
+            if (samplePatch.size() && samplePatch != "none")
             {
                 FatalErrorInFunction
                     << "No need to supply a patch name when in "
@@ -426,26 +550,24 @@ void Foam::mappedPatchBase::findSamples
             forAll(samples, sampleI)
             {
                 const point& sample = samples[sampleI];
+                nearInfoWorld& near = nearest[sampleI];
 
                 label facei = meshSearchEngine.findNearestFace(sample);
 
                 if (facei == -1)
                 {
-                    nearest[sampleI].second().first() = Foam::sqr(GREAT);
-                    nearest[sampleI].second().second() = Pstream::myProcNo();
+                    near.first().second().first() = Foam::sqr(GREAT);
+                    near.first().second().second() = myRank;
+                    near.second() = mySampleWorld;
                 }
                 else
                 {
                     const point& fc = mesh.faceCentres()[facei];
 
-                    nearest[sampleI].first() = pointIndexHit
-                    (
-                        true,
-                        fc,
-                        facei
-                    );
-                    nearest[sampleI].second().first() = magSqr(fc-sample);
-                    nearest[sampleI].second().second() = Pstream::myProcNo();
+                    near.first().first() = pointIndexHit(true, fc, facei);
+                    near.first().second().first() = magSqr(fc-sample);
+                    near.first().second().second() = myRank;
+                    near.second() = mySampleWorld;
                 }
             }
             break;
@@ -463,31 +585,133 @@ void Foam::mappedPatchBase::findSamples
                 << "problem." << abort(FatalError);
         }
     }
+}
 
 
-    // Find nearest. Combine on master.
-    Pstream::listCombineGather(nearest, nearestEqOp());
-    Pstream::listCombineScatter(nearest);
+void Foam::mappedPatchBase::findSamples
+(
+    const sampleMode mode,
+    const label myWorld,
+    const pointField& samples,
+    const labelList& wantedWorlds,
+    const labelList& origProcs,
+
+    labelList& sampleProcs,
+    labelList& sampleIndices,
+    pointField& sampleLocations
+) const
+{
+    // Find the processor/cell containing the samples. Does not account
+    // for samples being found in two processors.
 
 
-    if (debug)
+    const label myRank = Pstream::myProcNo(comm_);
+    const label nProcs = Pstream::nProcs(comm_);
+
+    wordList samplePatches(nProcs);
     {
-        InfoInFunction
-            << "mesh " << sampleRegion() << " : " << endl;
+        const label oldComm(Pstream::warnComm);
+        Pstream::warnComm = comm_;
+        samplePatches[myRank] = samplePatch_;
+        Pstream::gatherList(samplePatches, Pstream::msgType(), comm_);
+        Pstream::scatterList(samplePatches, Pstream::msgType(), comm_);
+        Pstream::warnComm = oldComm;
+    }
+    wordList sampleRegions(nProcs);
+    {
+        const label oldComm(Pstream::warnComm);
+        Pstream::warnComm = comm_;
+        sampleRegions[myRank] = sampleRegion_;
+        Pstream::gatherList(sampleRegions, Pstream::msgType(), comm_);
+        Pstream::scatterList(sampleRegions, Pstream::msgType(), comm_);
+        Pstream::warnComm = oldComm;
+    }
 
-        forAll(nearest, sampleI)
+    // Find all the info for nearest
+    List<nearInfoWorld> nearest(samples.size());
+    forAll(nearest, samplei)
+    {
+        nearest[samplei].first() = nearInfo
+        (
+            pointIndexHit(),
+            Tuple2<scalar, label>(Foam::sqr(GREAT), -1)
+        );
+        nearest[samplei].second() = wantedWorlds[samplei];
+    }
+
+
+    // Extract samples to search for locally
+    {
+        DynamicList<label> localMap(samples.size());
+        forAll(wantedWorlds, samplei)
         {
-            label proci = nearest[sampleI].second().second();
-            label localI = nearest[sampleI].first().index();
+            if (wantedWorlds[samplei] == myWorld)
+            {
+                localMap.append(samplei);
+            }
+        }
 
-            Info<< "    " << sampleI << " coord:"<< samples[sampleI]
-                << " found on processor:" << proci
-                << " in local cell/face/point:" << localI
-                << " with location:" << nearest[sampleI].first().rawPoint()
-                << endl;
+        if (localMap.size())
+        {
+            pointField localSamples(samples, localMap);
+            labelList localOrigProcs(origProcs, localMap);
+
+            //Assume single patch to sample for now
+            const word localOrigPatch(samplePatches[localOrigProcs[0]]);
+            const word localOrigRegion(sampleRegions[localOrigProcs[0]]);
+            List<nearInfoWorld> localNearest(localSamples.size());
+
+            if (debug)
+            {
+                Pout<< "Searching locally for " << localSamples.size()
+                    << " samples on region:" << localOrigRegion
+                    << " on patch:" << localOrigPatch << endl;
+            }
+            findLocalSamples
+            (
+                mode,
+                myWorld,
+                localOrigRegion,
+                localOrigPatch,
+                localSamples,
+                localNearest
+            );
+            UIndirectList<nearInfoWorld>(nearest, localMap) = localNearest;
         }
     }
 
+    const label oldComm(Pstream::warnComm);
+    Pstream::warnComm = comm_;
+
+    // Find nearest. Combine on master.
+    Pstream::listCombineGather
+    (
+        nearest,
+        nearestWorldEqOp(),
+        Pstream::msgType(),
+        comm_
+    );
+    Pstream::listCombineScatter(nearest, Pstream::msgType(), comm_);
+
+    //if (debug)
+    //{
+    //    Pout<< "** AFter combining:" << endl;
+    //    forAll(nearest, samplei)
+    //    {
+    //        Pout<< "  sample:" << samples[samplei]
+    //            << " origating from proc:" << origProcs[samplei]
+    //            << " to be found on world:" << wantedWorlds[samplei] << nl
+    //            << "    found on world:" << nearest[samplei].second() << nl
+    //            << "    found on proc:"
+    //            << nearest[samplei].first().second().second() << nl
+    //            << "    found on patchfacei:"
+    //            << nearest[samplei].first().first().index() << nl
+    //            << "    found at location:"
+    //            << nearest[samplei].first().first().rawPoint() << nl;
+    //    }
+    //    Pout<< endl;
+    //}
+
     // Convert back into proc+local index
     sampleProcs.setSize(samples.size());
     sampleIndices.setSize(samples.size());
@@ -495,7 +719,9 @@ void Foam::mappedPatchBase::findSamples
 
     forAll(nearest, sampleI)
     {
-        if (!nearest[sampleI].first().hit())
+        const nearInfo& ni = nearest[sampleI].first();
+
+        if (!ni.first().hit())
         {
             sampleProcs[sampleI] = -1;
             sampleIndices[sampleI] = -1;
@@ -503,11 +729,13 @@ void Foam::mappedPatchBase::findSamples
         }
         else
         {
-            sampleProcs[sampleI] = nearest[sampleI].second().second();
-            sampleIndices[sampleI] = nearest[sampleI].first().index();
-            sampleLocations[sampleI] = nearest[sampleI].first().hitPoint();
+            sampleProcs[sampleI] = ni.second().second();
+            sampleIndices[sampleI] = ni.first().index();
+            sampleLocations[sampleI] = ni.first().hitPoint();
         }
     }
+
+    Pstream::warnComm = oldComm;
 }
 
 
@@ -520,6 +748,31 @@ void Foam::mappedPatchBase::calcMapping() const
             << "Mapping already calculated" << exit(FatalError);
     }
 
+    //// Make sure if running in database that there is a syncObjects FO
+    //if (sampleDatabase() && !sameWorld())
+    //{
+    //    const word syncName("syncObjects");
+    //    const polyMesh& mesh = patch_.boundaryMesh().mesh();
+    //    const Time& runTime = mesh.time();
+    //    const functionObjectList& fos = runTime.functionObjects();
+    //
+    //    forAll(fos, i)
+    //    {
+    //        Pout<< "** FO:" << fos[i].name() << " tpye:" << fos[i].type()
+    //            << endl;
+    //    }
+    //
+    //    if (fos.findObjectID(syncName) == -1)
+    //    {
+    //        //FatalErrorInFunction
+    //        WarningInFunction
+    //            << "Did not detect functionObject " << syncName
+    //            << ". This is used to synchronise data inbetween worlds"
+    //            << endl;
+    //    }
+    //}
+
+
     // Get points on face (since cannot use face-centres - might be off
     // face-diagonal decomposed tets.
     tmp<pointField> patchPoints(facePoints(patch_));
@@ -532,50 +785,85 @@ void Foam::mappedPatchBase::calcMapping() const
     bool sampleMyself =
     (
         mode_ == NEARESTPATCHFACE
+     && sampleWorld() == UPstream::myWorld()
      && sampleRegion() == patch_.boundaryMesh().mesh().name()
      && samplePatch() == patch_.name()
     );
 
-    // Check offset
-    vectorField d(offsettedPoints-patchPoints());
-    bool coincident = (gAverage(mag(d)) <= ROOTVSMALL);
-
-    if (sampleMyself && coincident)
+    if (sampleMyself)
     {
-        WarningInFunction
-            << "Invalid offset " << d << endl
-            << "Offset is the vector added to the patch face centres to"
-            << " find the patch face supplying the data." << endl
-            << "Setting it to " << d
-            << " on the same patch, on the same region"
-            << " will find the faces themselves which does not make sense"
-            << " for anything but testing." << endl
-            << "patch_:" << patch_.name() << endl
-            << "sampleRegion_:" << sampleRegion() << endl
-            << "mode_:" << sampleModeNames_[mode_] << endl
-            << "samplePatch_:" << samplePatch() << endl
-            << "offsetMode_:" << offsetModeNames_[offsetMode_] << endl;
+        // Check offset
+        vectorField d(offsettedPoints-patchPoints());
+        bool coincident = (gAverage(mag(d)) <= ROOTVSMALL);
+
+        if (sampleMyself && coincident)
+        {
+            WarningInFunction
+                << "Invalid offset " << d << endl
+                << "Offset is the vector added to the patch face centres to"
+                << " find the patch face supplying the data." << endl
+                << "Setting it to " << d
+                << " on the same patch, on the same region"
+                << " will find the faces themselves which does not make sense"
+                << " for anything but testing." << endl
+                << "patch_:" << patch_.name() << endl
+                << "sampleRegion_:" << sampleRegion() << endl
+                << "mode_:" << sampleModeNames_[mode_] << endl
+                << "samplePatch_:" << samplePatch() << endl
+                << "offsetMode_:" << offsetModeNames_[offsetMode_] << endl;
+        }
     }
 
+    // Get local world and world-to-sample in index form
+    const label myWorld = Pstream::myWorldID();
+    const label mySampleWorld = Pstream::allWorlds().find(sampleWorld_);
+
+
     // Get global list of all samples and the processor and face they come from.
-    pointField samples;
-    labelList patchFaceProcs;
-    labelList patchFaces;
-    pointField patchFc;
+    pointField samples;         // coordinates
+    labelList patchFaceWorlds;  // world to sample
+    labelList patchFaceProcs;   // originating processor
+    labelList patchFaces;       // originating face on processor patch
+    pointField patchFc;         // originating face centre
     collectSamples
     (
+        mySampleWorld,          // world I want to sample
         patchPoints,
+
         samples,
+        patchFaceWorlds,
         patchFaceProcs,
         patchFaces,
         patchFc
     );
 
+    //if (debug)
+    //{
+    //    forAll(samples, samplei)
+    //    {
+    //        Pout<< "    sample:" << samples[samplei]
+    //            << " origating from proc:" << patchFaceProcs[samplei]
+    //            << "  face:" << patchFaces[samplei]
+    //            << " to be found on world:" << patchFaceWorlds[samplei] << nl;
+    //    }
+    //}
+
     // Find processor and cell/face samples are in and actual location.
     labelList sampleProcs;
     labelList sampleIndices;
     pointField sampleLocations;
-    findSamples(mode_, samples, sampleProcs, sampleIndices, sampleLocations);
+    findSamples
+    (
+        mode_,
+        myWorld,        // my world (in index form)
+        samples,
+        patchFaceWorlds,
+        patchFaceProcs,
+
+        sampleProcs,
+        sampleIndices,
+        sampleLocations
+    );
 
     // Check for samples that were not found. This will only happen for
     // NEARESTCELL since finds cell containing a location
@@ -589,7 +877,7 @@ void Foam::mappedPatchBase::calcMapping() const
                 nNotFound++;
             }
         }
-        reduce(nNotFound, sumOp<label>());
+        reduce(nNotFound, sumOp<label>(), Pstream::msgType(), comm_);
 
         if (nNotFound > 0)
         {
@@ -610,14 +898,11 @@ void Foam::mappedPatchBase::calcMapping() const
 
             // Collect the samples that cannot be found
             DynamicList<label> subMap;
-            DynamicField<point> subSamples;
-
             forAll(sampleProcs, sampleI)
             {
                 if (sampleProcs[sampleI] == -1)
                 {
                     subMap.append(sampleI);
-                    subSamples.append(samples[sampleI]);
                 }
             }
 
@@ -628,7 +913,12 @@ void Foam::mappedPatchBase::calcMapping() const
             findSamples
             (
                 NEARESTONLYCELL,
-                subSamples,
+                myWorld,        // my world (in index form)
+
+                pointField(samples, subMap),
+                UIndirectList<label>(patchFaceWorlds, subMap)(),
+                UIndirectList<label>(patchFaceProcs, subMap)(),
+
                 subSampleProcs,
                 subSampleIndices,
                 subSampleLocations
@@ -647,24 +937,39 @@ void Foam::mappedPatchBase::calcMapping() const
     // - cell/face sample is in (so source when mapping)
     //   sampleIndices, sampleProcs.
 
-    //forAll(samples, i)
-    //{
-    //    Info<< i << " need data in region "
-    //        << patch_.boundaryMesh().mesh().name()
-    //        << " for proc:" << patchFaceProcs[i]
-    //        << " face:" << patchFaces[i]
-    //        << " at:" << patchFc[i] << endl
-    //        << "Found data in region " << sampleRegion()
-    //        << " at proc:" << sampleProcs[i]
-    //        << " face:" << sampleIndices[i]
-    //        << " at:" << sampleLocations[i]
-    //        << nl << endl;
-    //}
-
-
-
-    if (debug && Pstream::master())
+    if (Pstream::master(comm_))
     {
+        forAll(samples, i)
+        {
+            if (sampleProcs[i] == -1)
+            {
+                FatalErrorInFunction << "did not find sample "
+                    << patchFc[i] << " on patch " << patch_.name()
+                    << " on region "
+                    << patch_.boundaryMesh().mesh().name()
+                    << " on processor " << patchFaceProcs[i]
+                    << exit(FatalError);
+            }
+        }
+    }
+
+
+    if (debug && Pstream::master(comm_))
+    {
+        //forAll(samples, i)
+        //{
+        //    Pout<< i << " need data in region "
+        //        << patch_.boundaryMesh().mesh().name()
+        //        << " for proc:" << patchFaceProcs[i]
+        //        << " face:" << patchFaces[i]
+        //        << " at:" << patchFc[i] << endl
+        //        << "Found data in region " << sampleRegion()
+        //        << " at proc:" << sampleProcs[i]
+        //        << " face:" << sampleIndices[i]
+        //        << " at:" << sampleLocations[i]
+        //        << nl << endl;
+        //}
+
         OFstream str
         (
             patch_.boundaryMesh().mesh().time().path()
@@ -688,7 +993,7 @@ void Foam::mappedPatchBase::calcMapping() const
     }
 
     // Determine schedule.
-    mapPtr_.reset(new mapDistribute(sampleProcs, patchFaceProcs));
+    mapPtr_.reset(new mapDistribute(sampleProcs, patchFaceProcs, comm_));
 
     // Rework the schedule from indices into samples to cell data to send,
     // face data to receive.
@@ -701,16 +1006,17 @@ void Foam::mappedPatchBase::calcMapping() const
         subMap[proci] = labelUIndList(sampleIndices, subMap[proci]);
         constructMap[proci] = labelUIndList(patchFaces, constructMap[proci]);
 
-        //if (debug)
-        //{
-        //    Pout<< "To proc:" << proci << " sending values of cells/faces:"
-        //        << subMap[proci] << endl;
-        //    Pout<< "From proc:" << proci
-        //        << " receiving values of patch faces:"
-        //        << constructMap[proci] << endl;
-        //}
+        if (debug)
+        {
+            Pout<< "To proc:" << proci << " sending values of cells/faces:"
+                << subMap[proci] << endl;
+            Pout<< "From proc:" << proci
+                << " receiving values of patch faces:"
+                << constructMap[proci] << endl;
+        }
     }
 
+
     // Redo constructSize
     mapPtr_().constructSize() = patch_.size();
 
@@ -798,36 +1104,97 @@ void Foam::mappedPatchBase::calcAMI() const
         return;
     }
 
-    const polyPatch& nbr = samplePolyPatch();
-
-    // Transform neighbour patch to local system
-    pointField nbrPoints(samplePoints(nbr.localPoints()));
-
-    primitivePatch nbrPatch0
-    (
-        SubList<face>
-        (
-            nbr.localFaces(),
-            nbr.size()
-        ),
-        nbrPoints
-    );
-
-
-    if (debug)
+    // Check if running locally
+    if (sampleWorld_.empty())
     {
-        OFstream os(patch_.name() + "_neighbourPatch-org.obj");
-        meshTools::writeOBJ(os, samplePolyPatch().localFaces(), nbrPoints);
+        const polyPatch& nbr = samplePolyPatch();
 
-        OFstream osN(patch_.name() + "_neighbourPatch-trans.obj");
-        meshTools::writeOBJ(osN, nbrPatch0, nbrPoints);
+        // Transform neighbour patch to local system
+        pointField nbrPoints(samplePoints(nbr.localPoints()));
 
-        OFstream osO(patch_.name() + "_ownerPatch.obj");
-        meshTools::writeOBJ(osO, patch_.localFaces(), patch_.localPoints());
+        primitivePatch nbrPatch0
+        (
+            SubList<face>
+            (
+                nbr.localFaces(),
+                nbr.size()
+            ),
+            nbrPoints
+        );
+
+
+        if (debug)
+        {
+            OFstream os(patch_.name() + "_neighbourPatch-org.obj");
+            meshTools::writeOBJ(os, samplePolyPatch().localFaces(), nbrPoints);
+
+            OFstream osN(patch_.name() + "_neighbourPatch-trans.obj");
+            meshTools::writeOBJ(osN, nbrPatch0, nbrPoints);
+
+            OFstream osO(patch_.name() + "_ownerPatch.obj");
+            meshTools::writeOBJ(osO, patch_.localFaces(), patch_.localPoints());
+        }
+
+        // Construct/apply AMI interpolation to determine addressing and weights
+        AMIPtr_->calculate(patch_, nbrPatch0, surfPtr());
     }
+    else
+    {
+        faceList nbrFaces;
+        pointField nbrPoints;
+        if (sampleWorld() == UPstream::myWorld())
+        {
+            const polyPatch& nbr = samplePolyPatch();
+            nbrFaces = nbr.localFaces();
+            nbrPoints = samplePoints(nbr.localPoints());
+        }
+        else
+        {
+            // Leave empty
+        }
 
-    // Construct/apply AMI interpolation to determine addressing and weights
-    AMIPtr_->calculate(patch_, nbrPatch0, surfPtr());
+        primitivePatch nbrPatch0
+        (
+            SubList<face>
+            (
+                nbrFaces,
+                nbrFaces.size()
+            ),
+            nbrPoints
+        );
+
+        // Change to use ALL processors communicator
+        const label oldWorldComm = Pstream::worldComm;
+        Pstream::worldComm = comm_;
+
+        const label oldComm(Pstream::warnComm);
+        Pstream::warnComm = UPstream::worldComm;
+
+        // Construct/apply AMI interpolation to determine addressing and weights
+        AMIPtr_->calculate(patch_, nbrPatch0, surfPtr());
+
+        Pstream::warnComm = oldComm;
+        Pstream::worldComm = oldWorldComm;
+    }
+}
+
+
+const Foam::objectRegistry& Foam::mappedPatchBase::subRegistry
+(
+    const objectRegistry& obr,
+    const wordList& names,
+    const label index
+)
+{
+    const objectRegistry& sub = obr.subRegistry(names[index], true);
+    if (index == names.size()-1)
+    {
+        return sub;
+    }
+    else
+    {
+        return subRegistry(sub, names, index+1);
+    }
 }
 
 
@@ -836,15 +1203,22 @@ void Foam::mappedPatchBase::calcAMI() const
 Foam::mappedPatchBase::mappedPatchBase(const polyPatch& pp)
 :
     patch_(pp),
+    sampleWorld_(word::null),
     sampleRegion_(patch_.boundaryMesh().mesh().name()),
     mode_(NEARESTPATCHFACE),
-    samplePatch_(""),
+    samplePatch_(word::null),
     coupleGroup_(),
+    sampleDatabasePtr_(),
     offsetMode_(UNIFORM),
     offset_(Zero),
     offsets_(pp.size(), offset_),
     distance_(0),
-    sameRegion_(sampleRegion_ == patch_.boundaryMesh().mesh().name()),
+    comm_(communicator(sampleWorld_)),
+    sameRegion_
+    (
+        sampleWorld_.empty()
+     && sampleRegion_ == patch_.boundaryMesh().mesh().name()
+    ),
     mapPtr_(nullptr),
     AMIReverse_(false),
     AMIPtr_(new faceAreaWeightAMI(true, AMIReverse_)),
@@ -863,15 +1237,22 @@ Foam::mappedPatchBase::mappedPatchBase
 )
 :
     patch_(pp),
+    sampleWorld_(word::null),
     sampleRegion_(sampleRegion),
     mode_(mode),
     samplePatch_(samplePatch),
     coupleGroup_(),
+    sampleDatabasePtr_(),
     offsetMode_(NONUNIFORM),
     offset_(Zero),
     offsets_(offsets),
     distance_(0),
-    sameRegion_(sampleRegion_ == patch_.boundaryMesh().mesh().name()),
+    comm_(communicator(sampleWorld_)),
+    sameRegion_
+    (
+        sampleWorld_.empty()
+     && sampleRegion_ == patch_.boundaryMesh().mesh().name()
+    ),
     mapPtr_(nullptr),
     AMIReverse_(false),
     AMIPtr_(new faceAreaWeightAMI(true, AMIReverse_)),
@@ -890,15 +1271,22 @@ Foam::mappedPatchBase::mappedPatchBase
 )
 :
     patch_(pp),
+    sampleWorld_(word::null),
     sampleRegion_(sampleRegion),
     mode_(mode),
     samplePatch_(samplePatch),
     coupleGroup_(),
+    sampleDatabasePtr_(),
     offsetMode_(UNIFORM),
     offset_(offset),
     offsets_(0),
     distance_(0),
-    sameRegion_(sampleRegion_ == patch_.boundaryMesh().mesh().name()),
+    comm_(communicator(sampleWorld_)),
+    sameRegion_
+    (
+        sampleWorld_.empty()
+     && sampleRegion_ == patch_.boundaryMesh().mesh().name()
+    ),
     mapPtr_(nullptr),
     AMIReverse_(false),
     AMIPtr_(new faceAreaWeightAMI(true, AMIReverse_)),
@@ -917,15 +1305,22 @@ Foam::mappedPatchBase::mappedPatchBase
 )
 :
     patch_(pp),
+    sampleWorld_(word::null),
     sampleRegion_(sampleRegion),
     mode_(mode),
     samplePatch_(samplePatch),
     coupleGroup_(),
+    sampleDatabasePtr_(),
     offsetMode_(NORMAL),
     offset_(Zero),
     offsets_(0),
     distance_(distance),
-    sameRegion_(sampleRegion_ == patch_.boundaryMesh().mesh().name()),
+    comm_(communicator(sampleWorld_)),
+    sameRegion_
+    (
+        sampleWorld_.empty()
+     && sampleRegion_ == patch_.boundaryMesh().mesh().name()
+    ),
     mapPtr_(nullptr),
     AMIReverse_(false),
     AMIPtr_(new faceAreaWeightAMI(true, AMIReverse_)),
@@ -941,15 +1336,22 @@ Foam::mappedPatchBase::mappedPatchBase
 )
 :
     patch_(pp),
-    sampleRegion_(dict.getOrDefault<word>("sampleRegion", "")),
+    sampleWorld_(dict.getOrDefault<word>("sampleWorld", word::null)),
+    sampleRegion_(dict.getOrDefault<word>("sampleRegion", word::null)),
     mode_(sampleModeNames_.get("sampleMode", dict)),
-    samplePatch_(dict.getOrDefault<word>("samplePatch", "")),
+    samplePatch_(dict.getOrDefault<word>("samplePatch", word::null)),
     coupleGroup_(dict),
+    sampleDatabasePtr_(readDatabase(dict)),
     offsetMode_(UNIFORM),
     offset_(Zero),
-    offsets_(),
-    distance_(0),
-    sameRegion_(sampleRegion_ == patch_.boundaryMesh().mesh().name()),
+    offsets_(0),
+    distance_(0.0),
+    comm_(communicator(sampleWorld_)),
+    sameRegion_
+    (
+        sampleWorld_.empty()
+     && sampleRegion_ == patch_.boundaryMesh().mesh().name()
+    ),
     mapPtr_(nullptr),
     AMIReverse_(dict.getOrDefault("flipNormals", false)),
     AMIPtr_
@@ -966,7 +1368,7 @@ Foam::mappedPatchBase::mappedPatchBase
 {
     if (!coupleGroup_.valid())
     {
-        if (sampleRegion_.empty())
+        if (sampleWorld_.empty() && sampleRegion_.empty())
         {
             // If no coupleGroup and no sampleRegion assume local region
             sampleRegion_ = patch_.boundaryMesh().mesh().name();
@@ -1024,15 +1426,22 @@ Foam::mappedPatchBase::mappedPatchBase
 )
 :
     patch_(pp),
-    sampleRegion_(dict.getOrDefault<word>("sampleRegion", "")),
+    sampleWorld_(dict.getOrDefault<word>("sampleWorld", word::null)),
+    sampleRegion_(dict.getOrDefault<word>("sampleRegion", word::null)),
     mode_(mode),
-    samplePatch_(dict.getOrDefault<word>("samplePatch", "")),
-    coupleGroup_(dict), //dict.getOrDefault<word>("coupleGroup", "")),
+    samplePatch_(dict.getOrDefault<word>("samplePatch", word::null)),
+    coupleGroup_(dict), //dict.getOrDefault<word>("coupleGroup", word::null)),
+    sampleDatabasePtr_(readDatabase(dict)),
     offsetMode_(UNIFORM),
     offset_(Zero),
     offsets_(0),
-    distance_(0),
-    sameRegion_(sampleRegion_ == patch_.boundaryMesh().mesh().name()),
+    distance_(0.0),
+    comm_(communicator(sampleWorld_)),
+    sameRegion_
+    (
+        sampleWorld_.empty()
+     && sampleRegion_ == patch_.boundaryMesh().mesh().name()
+    ),
     mapPtr_(nullptr),
     AMIReverse_(dict.getOrDefault("flipNormals", false)),
     AMIPtr_
@@ -1060,7 +1469,7 @@ Foam::mappedPatchBase::mappedPatchBase
 
     if (!coupleGroup_.valid())
     {
-        if (sampleRegion_.empty())
+        if (sampleWorld_.empty() && sampleRegion_.empty())
         {
             // If no coupleGroup and no sampleRegion assume local region
             sampleRegion_ = patch_.boundaryMesh().mesh().name();
@@ -1077,14 +1486,22 @@ Foam::mappedPatchBase::mappedPatchBase
 )
 :
     patch_(pp),
+    sampleWorld_(mpb.sampleWorld_),
     sampleRegion_(mpb.sampleRegion_),
     mode_(mpb.mode_),
     samplePatch_(mpb.samplePatch_),
     coupleGroup_(mpb.coupleGroup_),
+    sampleDatabasePtr_
+    (
+        mpb.sampleDatabasePtr_
+      ? new fileName(mpb.sampleDatabasePtr_())
+      : nullptr
+    ),
     offsetMode_(mpb.offsetMode_),
     offset_(mpb.offset_),
     offsets_(mpb.offsets_),
     distance_(mpb.distance_),
+    comm_(mpb.comm_),
     sameRegion_(mpb.sameRegion_),
     mapPtr_(nullptr),
     AMIReverse_(mpb.AMIReverse_),
@@ -1102,10 +1519,17 @@ Foam::mappedPatchBase::mappedPatchBase
 )
 :
     patch_(pp),
+    sampleWorld_(mpb.sampleWorld_),
     sampleRegion_(mpb.sampleRegion_),
     mode_(mpb.mode_),
     samplePatch_(mpb.samplePatch_),
     coupleGroup_(mpb.coupleGroup_),
+    sampleDatabasePtr_
+    (
+        mpb.sampleDatabasePtr_
+      ? new fileName(mpb.sampleDatabasePtr_())
+      : nullptr
+    ),
     offsetMode_(mpb.offsetMode_),
     offset_(mpb.offset_),
     offsets_
@@ -1115,6 +1539,7 @@ Foam::mappedPatchBase::mappedPatchBase
       : vectorField()
     ),
     distance_(mpb.distance_),
+    comm_(mpb.comm_),
     sameRegion_(mpb.sameRegion_),
     mapPtr_(nullptr),
     AMIReverse_(mpb.AMIReverse_),
@@ -1142,19 +1567,55 @@ void Foam::mappedPatchBase::clearOut()
 
 // * * * * * * * * * * * * * * * Member Functions  * * * * * * * * * * * * * //
 
-const Foam::polyMesh& Foam::mappedPatchBase::sampleMesh() const
+const Foam::polyMesh& Foam::mappedPatchBase::lookupMesh
+(
+    const word& sampleRegion
+) const
 {
     const polyMesh& thisMesh = patch_.boundaryMesh().mesh();
-
     return
     (
-        sameRegion_
+        sampleRegion.empty() || sampleRegion == thisMesh.name()
       ? thisMesh
-      : thisMesh.time().lookupObject<polyMesh>(sampleRegion())
+      : thisMesh.time().lookupObject<polyMesh>(sampleRegion)
     );
 }
 
 
+const Foam::polyPatch& Foam::mappedPatchBase::lookupPatch
+(
+    const word& sampleRegion,
+    const word& samplePatch
+) const
+{
+    const polyMesh& nbrMesh = lookupMesh(sampleRegion);
+
+    const label patchi = nbrMesh.boundaryMesh().findPatchID(samplePatch);
+
+    if (patchi == -1)
+    {
+        FatalErrorInFunction
+            << "Cannot find patch " << samplePatch
+            << " in region " << sampleRegion_ << endl
+            << exit(FatalError);
+    }
+    return nbrMesh.boundaryMesh()[patchi];
+}
+
+
+const Foam::polyMesh& Foam::mappedPatchBase::sampleMesh() const
+{
+    if (UPstream::myWorld() != sampleWorld_)
+    {
+        FatalErrorInFunction
+            << "sampleWorld : " << sampleWorld_
+            << " is not the current world : " << UPstream::myWorld()
+            << exit(FatalError);
+    }
+    return lookupMesh(sampleRegion());
+}
+
+
 const Foam::polyPatch& Foam::mappedPatchBase::samplePolyPatch() const
 {
     const polyMesh& nbrMesh = sampleMesh();
@@ -1296,16 +1757,161 @@ Foam::pointIndexHit Foam::mappedPatchBase::facePoint
 }
 
 
+const Foam::objectRegistry& Foam::mappedPatchBase::subRegistry
+(
+    const objectRegistry& obr,
+    const fileName& rawFName
+)
+{
+    // Lookup (and create if non existing) a registry using a '/' separated
+    // path.
+
+    const fileName fName(rawFName.clean());
+    const wordList names(fName.components());
+
+    if (names.empty())
+    {
+        return obr;
+    }
+    else
+    {
+        return subRegistry(obr, names, 0);
+    }
+}
+
+
+Foam::fileName Foam::mappedPatchBase::sendPath
+(
+    const fileName& root,
+    const label proci
+)
+{
+    const word processorName("processor"+Foam::name(proci));
+    return root/"send"/processorName;
+}
+
+
+Foam::fileName Foam::mappedPatchBase::sendPath(const label proci) const
+{
+    return sendPath(sampleDatabasePath(), proci);
+}
+
+
+Foam::fileName Foam::mappedPatchBase::receivePath
+(
+    const fileName& root,
+    const label proci
+)
+{
+    const word processorName("processor"+Foam::name(proci));
+    return root/"receive"/processorName;
+}
+
+
+Foam::fileName Foam::mappedPatchBase::receivePath(const label proci) const
+{
+    return receivePath(sampleDatabasePath(), proci);
+}
+
+
+void Foam::mappedPatchBase::writeDict
+(
+    const objectRegistry& obr,
+    dictionary& dict
+)
+{
+    forAllIters(obr, iter)
+    {
+        regIOobject* objPtr = iter.val();
+        const regIOobject& obj = *objPtr;
+
+        if (isA<objectRegistry>(obj))
+        {
+            dictionary& d = dict.subDictOrAdd(obj.name());
+            writeDict(dynamic_cast<const objectRegistry&>(obj), d);
+        }
+        else if
+        (
+            writeIOField<scalar>(obj, dict)
+         || writeIOField<vector>(obj, dict)
+         || writeIOField<sphericalTensor>(obj, dict)
+         || writeIOField<symmTensor>(obj, dict)
+         || writeIOField<tensor>(obj, dict)
+        )
+        {
+            // IOField specialisation
+        }
+        else
+        {
+            // Not tested. No way of retrieving data anyway ...
+            OTstream os;
+            obj.writeData(os);
+
+            primitiveEntry* pePtr = new primitiveEntry(obj.name(), os.tokens());
+            dict.add(pePtr);
+        }
+    }
+}
+
+
+void Foam::mappedPatchBase::readDict(const dictionary& d, objectRegistry& obr)
+{
+    // Reverse of writeDict - reads fields from dictionary into objectRegistry
+    for (const entry& e : d)
+    {
+        if (e.isDict())
+        {
+            // Add sub registry
+            objectRegistry& sub = const_cast<objectRegistry&>
+            (
+                obr.subRegistry(e.keyword(), true)
+            );
+
+            readDict(e.dict(), sub);
+        }
+        else
+        {
+            ITstream& is = e.stream();
+            token tok(is);
+
+            if
+            (
+                constructIOField<scalar>(e.keyword(), tok, is, obr)
+             || constructIOField<vector>(e.keyword(), tok, is, obr)
+             || constructIOField<sphericalTensor>(e.keyword(), tok, is, obr)
+             || constructIOField<symmTensor>(e.keyword(), tok, is, obr)
+             || constructIOField<tensor>(e.keyword(), tok, is, obr)
+            )
+            {
+                // Done storing field
+            }
+            else
+            {
+                FatalErrorInFunction << "Unsupported type " << e.keyword()
+                    << exit(FatalError);
+            }
+        }
+    }
+}
+
+
 void Foam::mappedPatchBase::write(Ostream& os) const
 {
     os.writeEntry("sampleMode", sampleModeNames_[mode_]);
-    if (!sampleRegion_.empty())
+    os.writeEntryIfDifferent<word>("sampleWorld", word::null, sampleWorld_);
+    os.writeEntryIfDifferent<word>("sampleRegion", word::null, sampleRegion_);
+    os.writeEntryIfDifferent<word>("samplePatch", word::null, samplePatch_);
+
+    if (sampleDatabasePtr_)
     {
-        os.writeEntry("sampleRegion", sampleRegion_);
-    }
-    if (!samplePatch_.empty())
-    {
-        os.writeEntry("samplePatch", samplePatch_);
+        os.writeEntry("sampleDatabase", sampleDatabasePtr_.valid());
+        // Write database path if differing
+        os.writeEntryIfDifferent<fileName>
+        (
+            "sampleDatabasePath",
+            fileName::null,
+            sampleDatabasePtr_()
+        );
     }
     coupleGroup_.write(os);
 
diff --git a/src/meshTools/mappedPatches/mappedPolyPatch/mappedPatchBase.H b/src/meshTools/mappedPatches/mappedPolyPatch/mappedPatchBase.H
index d6b76023db..deed76ff46 100644
--- a/src/meshTools/mappedPatches/mappedPolyPatch/mappedPatchBase.H
+++ b/src/meshTools/mappedPatches/mappedPolyPatch/mappedPatchBase.H
@@ -33,6 +33,13 @@ Description
 
     If constructed from dictionary:
     \verbatim
+        // Optional world to sample (default is all)
+        //sampleWorld solidSim;
+
+        // Optional explicit coupling (requires functionObject to synchronise
+        // databases. Default is close coupling (bc to bc)
+        //sampleDatabase true;
+
         // Region to sample (default is region0)
         sampleRegion region0;
 
@@ -184,6 +191,38 @@ public:
     };
 
 
+    //- nearest + world
+    //  Used to only look at entries from same world
+    typedef Tuple2<nearInfo, label> nearInfoWorld;
+
+    class nearestWorldEqOp
+    {
+
+    public:
+
+        void operator()(nearInfoWorld& x, const nearInfoWorld& y) const
+        {
+            // Is there a hit and is it sampling the same world
+            const nearInfo& xi = x.first();
+            const nearInfo& yi = y.first();
+            if (yi.first().hit())
+            {
+                if (x.second() == y.second())
+                {
+                    if (!xi.first().hit())
+                    {
+                        x = y;
+                    }
+                    else if (yi.second().first() < xi.second().first())
+                    {
+                        x = y;
+                    }
+                }
+            }
+        }
+    };
+
+
 protected:
 
     // Protected data
@@ -191,6 +230,9 @@ protected:
         //- Patch to sample
         const polyPatch& patch_;
 
+        //- World to sample
+        mutable word sampleWorld_;
+
         //- Region to sample
         mutable word sampleRegion_;
 
@@ -203,6 +245,9 @@ protected:
         //- PatchGroup (if in sampleMode NEARESTPATCH*)
         const coupleGroupIdentifier coupleGroup_;
 
+        //- Empty or location of database
+        const autoPtr<fileName> sampleDatabasePtr_;
+
         //- How to obtain samples
         offsetMode offsetMode_;
 
@@ -215,6 +260,9 @@ protected:
         //- Offset distance (normal)
         scalar distance_;
 
+        //- Communicator
+        label comm_;
+
         //- Same region
         mutable bool sameRegion_;
 
@@ -246,25 +294,59 @@ protected:
 
     // Protected Member Functions
 
+        //- Optionally allocate a world-local communicator
+        static label communicator(const word& sampleWorld);
+
+        //- Lookup mesh
+        const polyMesh& lookupMesh(const word& region) const;
+
+        //- Lookup patch
+        const polyPatch& lookupPatch
+        (
+            const word& sampleRegion,
+            const word& samplePatch
+        ) const;
+
+
         //- Get the points from face-centre-decomposition face centres
         //  and project them onto the face-diagonal-decomposition triangles.
         tmp<pointField> facePoints(const polyPatch&) const;
 
-        //- Collect single list of samples and originating processor+face.
+        //- Collect single list of samples and originating processor+face + 
+        //  wanted world
         void collectSamples
         (
+            const label mySampleWorld,  // My wanted sampling world
             const pointField& facePoints,
-            pointField&,
-            labelList& patchFaceProcs,
-            labelList& patchFaces,
+            pointField& samples,        // Per sample: coordinate
+            labelList& patchFaceWorlds, // Per sample: wanted world
+            labelList& patchFaceProcs,  // Per sample: originating proc
+            labelList& patchFaces,      // Per sample: originating face
             pointField& patchFc
         ) const;
 
-        //- Find cells/faces containing samples
+        //- Find (local) cells/faces containing samples
+        void findLocalSamples
+        (
+            const sampleMode mode,
+            const label sampleWorld,        // my world as index
+            const word& sampleRegion,
+            const word& samplePatch,
+            const pointField& samplePoints,
+
+            List<nearInfoWorld>& nearest
+        ) const;
+
+        //- Find (global) cells/faces containing samples
         void findSamples
         (
             const sampleMode mode,      // search mode
+            const label myWorldIndex,   // my world (in index form)
+
             const pointField&,
+            const labelList& wantedWorlds,
+            const labelList& origProcs, // per sample the originating proc
+
             labelList& sampleProcs,     // processor containing sample
             labelList& sampleIndices,   // local index of cell/face
             pointField& sampleLocations // actual representative location
@@ -280,6 +362,38 @@ protected:
         void calcAMI() const;
 
 
+        // Database handling
+
+            //- Read optional database name from dictionary
+            static autoPtr<fileName> readDatabase(const dictionary& dict);
+
+            //- Lookup (sub)objectRegistry by following names of sub registries.
+            //- Creates non-existing intermediate ones.
+            static const objectRegistry& subRegistry
+            (
+                const objectRegistry& obr,
+                const wordList& names,
+                const label index
+            );
+
+            //- Attempt to detect an IOField<Type> and write to dictionary
+            template<class Type>
+            static bool writeIOField
+            (
+                const regIOobject& obj,
+                dictionary& dict
+            );
+
+            //- Attempt to read an IOField<Type> and store on objectRegistry
+            template<class Type>
+            static bool constructIOField
+            (
+                const word& name,
+                token& tok,
+                Istream& is,
+                objectRegistry& obr
+            );
+
 public:
 
     //- Runtime type information
@@ -289,7 +403,7 @@ public:
     // Constructors
 
         //- Construct from patch
-        mappedPatchBase(const polyPatch&);
+        explicit mappedPatchBase(const polyPatch&);
 
         //- Construct with offsetMode=non-uniform
         mappedPatchBase
@@ -354,6 +468,9 @@ public:
             //- What to sample
             inline const sampleMode& mode() const;
 
+            //- World to sample
+            inline const word& sampleWorld() const;
+
             //- Region to sample
             inline const word& sampleRegion() const;
 
@@ -372,6 +489,12 @@ public:
             //- Offset vector (from patch faces to destination mesh objects)
             inline const vectorField& offsets() const;
 
+            //- Communicator
+            inline label comm() const;
+
+            //- Is world the local world
+            inline bool sameWorld() const;
+
             //- Cached sampleRegion != mesh.name()
             inline bool sameRegion() const;
 
@@ -412,6 +535,60 @@ public:
                 const polyMesh::cellDecomposition
             );
 
+        // For database storage
+
+            inline const fileName& sampleDatabasePath() const
+            {
+                return *sampleDatabasePtr_;
+            }
+
+            inline bool sampleDatabase() const
+            {
+                return sampleDatabasePtr_.valid();
+            }
+
+            //- Helper: return path to store data to be sent to processor i
+            static fileName sendPath(const fileName& root, const label proci);
+
+            virtual fileName sendPath(const label proci) const;
+
+            //- Helper: return path to store data to be received from
+            //- processor i
+            static fileName receivePath
+            (
+                const fileName& root,
+                const label proci
+            );
+
+            virtual fileName receivePath(const label proci) const;
+
+            //- Lookup (sub)objectRegistry from '/' separated path (relative to
+            //- objectRegistry). Creates non-existing intermediate ones.
+            static const objectRegistry& subRegistry
+            (
+                const objectRegistry& obr,
+                const fileName& path
+            );
+
+            //- Store an IOField on the objectRegistry relative to obr
+            template<class Type>
+            static void storeField
+            (
+                objectRegistry& obr,
+                const word& fieldName,
+                const Field<Type>& values
+            );
+
+            //- Convert objectRegistry contents into dictionary
+            static void writeDict
+            (
+                const objectRegistry& obr,
+                dictionary& dict
+            );
+
+            //- (recursively) construct and register IOFields from dictionary
+            static void readDict(const dictionary& d, objectRegistry& obr);
+
 
         // Distribute
 
diff --git a/src/meshTools/mappedPatches/mappedPolyPatch/mappedPatchBaseI.H b/src/meshTools/mappedPatches/mappedPolyPatch/mappedPatchBaseI.H
index f8bc08307c..d89e3fb15f 100644
--- a/src/meshTools/mappedPatches/mappedPolyPatch/mappedPatchBaseI.H
+++ b/src/meshTools/mappedPatches/mappedPolyPatch/mappedPatchBaseI.H
@@ -33,6 +33,12 @@ Foam::mappedPatchBase::mode() const
 }
 
 
+inline const Foam::word& Foam::mappedPatchBase::sampleWorld() const
+{
+    return sampleWorld_;
+}
+
+
 inline const Foam::word& Foam::mappedPatchBase::sampleRegion() const
 {
     if (sampleRegion_.empty())
@@ -138,6 +144,20 @@ inline const Foam::vectorField& Foam::mappedPatchBase::offsets() const
 }
 
 
+inline Foam::label Foam::mappedPatchBase::comm() const
+{
+    return comm_;
+}
+
+
+inline bool Foam::mappedPatchBase::sameWorld() const
+{
+    return
+        UPstream::allWorlds().size() == 1
+     || UPstream::myWorld() == sampleWorld_;
+}
+
+
 inline bool Foam::mappedPatchBase::sameRegion() const
 {
     return sameRegion_;
@@ -147,7 +167,9 @@ inline bool Foam::mappedPatchBase::sameRegion() const
 inline const Foam::mapDistribute& Foam::mappedPatchBase::map() const
 {
     const polyMesh& thisMesh = patch_.boundaryMesh().mesh();
-    bool topoChange = sampleMesh().topoChanging() || thisMesh.topoChanging();
+    bool topoChange =
+        (sameWorld() && sampleMesh().topoChanging())
+     || thisMesh.topoChanging();
 
     if (topoChange)
     {
@@ -169,7 +191,9 @@ inline const Foam::AMIPatchToPatchInterpolation& Foam::mappedPatchBase::AMI
 ) const
 {
     const polyMesh& thisMesh = patch_.boundaryMesh().mesh();
-    bool topoChange = sampleMesh().topoChanging() || thisMesh.topoChanging();
+    bool topoChange =
+        (sameWorld() && sampleMesh().topoChanging())
+     || thisMesh.topoChanging();
 
     if (topoChange || forceUpdate)
     {
diff --git a/src/meshTools/mappedPatches/mappedPolyPatch/mappedPatchBaseTemplates.C b/src/meshTools/mappedPatches/mappedPolyPatch/mappedPatchBaseTemplates.C
index 6595502577..66a4748c2d 100644
--- a/src/meshTools/mappedPatches/mappedPolyPatch/mappedPatchBaseTemplates.C
+++ b/src/meshTools/mappedPatches/mappedPolyPatch/mappedPatchBaseTemplates.C
@@ -28,11 +28,16 @@ License
 template<class Type>
 void Foam::mappedPatchBase::distribute(List<Type>& lst) const
 {
+    const label oldComm(Pstream::warnComm);
+    Pstream::warnComm = map().comm();
     switch (mode_)
     {
         case NEARESTPATCHFACEAMI:
         {
+            const label oldWorldComm = Pstream::worldComm;
+            Pstream::worldComm = comm_;
             lst = AMI().interpolateToSource(Field<Type>(std::move(lst)));
+            Pstream::worldComm = oldWorldComm;
             break;
         }
         default:
@@ -40,6 +45,7 @@ void Foam::mappedPatchBase::distribute(List<Type>& lst) const
             map().distribute(lst);
         }
     }
+    Pstream::warnComm = oldComm;
 }
 
 
@@ -50,11 +56,16 @@ void Foam::mappedPatchBase::distribute
     const CombineOp& cop
 ) const
 {
+    const label oldComm(Pstream::warnComm);
+    Pstream::warnComm = comm_;
     switch (mode_)
     {
         case NEARESTPATCHFACEAMI:
         {
+            const label oldWorldComm = Pstream::worldComm;
+            Pstream::worldComm = comm_;
             lst = AMI().interpolateToSource(Field<Type>(std::move(lst)), cop);
+            Pstream::worldComm = oldWorldComm;
             break;
         }
         default:
@@ -69,23 +80,31 @@ void Foam::mappedPatchBase::distribute
                 map().constructMap(),
                 false,
                 lst,
+                Type(Zero),
                 cop,
                 flipOp(),
-                Type(Zero)
+                UPstream::msgType(),
+                comm_
             );
         }
     }
+    Pstream::warnComm = oldComm;
 }
 
 
 template<class Type>
 void Foam::mappedPatchBase::reverseDistribute(List<Type>& lst) const
 {
+    const label oldComm(Pstream::warnComm);
+    Pstream::warnComm = map().comm();
     switch (mode_)
     {
         case NEARESTPATCHFACEAMI:
         {
+            const label oldWorldComm = Pstream::worldComm;
+            Pstream::worldComm = comm_;
             lst = AMI().interpolateToTarget(Field<Type>(std::move(lst)));
+            Pstream::worldComm = oldWorldComm;
             break;
         }
         default:
@@ -94,6 +113,7 @@ void Foam::mappedPatchBase::reverseDistribute(List<Type>& lst) const
             break;
         }
     }
+    Pstream::warnComm = oldComm;
 }
 
 
@@ -104,11 +124,16 @@ void Foam::mappedPatchBase::reverseDistribute
     const CombineOp& cop
 ) const
 {
+    const label oldComm(Pstream::warnComm);
+    Pstream::warnComm = map().comm();
     switch (mode_)
     {
         case NEARESTPATCHFACEAMI:
         {
+            const label oldWorldComm = Pstream::worldComm;
+            Pstream::worldComm = comm_;
             lst = AMI().interpolateToTarget(Field<Type>(std::move(lst)), cop);
+            Pstream::worldComm = oldWorldComm;
             break;
         }
         default:
@@ -124,13 +149,137 @@ void Foam::mappedPatchBase::reverseDistribute
                 map().subMap(),
                 false,
                 lst,
+                Type(Zero),
                 cop,
                 flipOp(),
-                Type(Zero)
+                UPstream::msgType(),
+                comm_
             );
             break;
         }
     }
+    Pstream::warnComm = oldComm;
+}
+
+
+template<class Type>
+bool Foam::mappedPatchBase::writeIOField
+(
+    const regIOobject& obj,
+    dictionary& dict
+)
+{
+    const auto* fldPtr = isA<IOField<Type>>(obj);
+    if (fldPtr)
+    {
+        const auto& fld = *fldPtr;
+
+        token tok;
+        tok = new token::Compound<List<Type>>(fld);
+
+        primitiveEntry* pePtr = new primitiveEntry
+        (
+            fld.name(),
+            tokenList
+            (
+                one(),
+                std::move(tok)
+            )
+        );
+
+        dict.set(pePtr);
+        return true;
+    }
+    else
+    {
+        return false;
+    }
+}
+
+
+template<class Type>
+bool Foam::mappedPatchBase::constructIOField
+(
+    const word& name,
+    token& tok,
+    Istream& is,
+    objectRegistry& obr
+)
+{
+    const word tag = "List<" + word(pTraits<Type>::typeName) + '>';
+
+    if (tok.isCompound() && tok.compoundToken().type() == tag)
+    {
+        IOField<Type>* fldPtr = obr.findObject<IOField<Type>>(name);
+        if (fldPtr)
+        {
+            fldPtr->transfer
+            (
+                dynamicCast<token::Compound<List<Type>>>
+                (
+                    tok.transferCompoundToken(is)
+                )
+            );
+        }
+        else
+        {
+            IOField<Type>* fldPtr = new IOField<Type>
+            (
+                IOobject
+                (
+                    name,
+                    obr,
+                    IOobject::NO_READ,
+                    IOobject::NO_WRITE
+                ),
+                0
+            );
+            fldPtr->transfer
+            (
+                dynamicCast<token::Compound<List<Type>>>
+                (
+                    tok.transferCompoundToken(is)
+                )
+            );
+            objectRegistry::store(fldPtr);
+        }
+        return true;
+    }
+    else
+    {
+        return false;
+    }
+}
+
+
+template<class Type>
+void Foam::mappedPatchBase::storeField
+(
+    objectRegistry& obr,
+    const word& fieldName,
+    const Field<Type>& values
+)
+{
+    IOField<Type>* fldPtr = obr.findObject<IOField<Type>>(fieldName);
+    if (fldPtr)
+    {
+        *fldPtr = values;
+    }
+    else
+    {
+        fldPtr = new IOField<Type>
+        (
+            IOobject
+            (
+                fieldName,
+                obr,
+                IOobject::NO_READ,
+                IOobject::NO_WRITE
+            ),
+            values
+        );
+        objectRegistry::store(fldPtr);
+    }
 }
 
 
diff --git a/src/overset/cellCellStencil/inverseDistance/inverseDistanceCellCellStencil.C b/src/overset/cellCellStencil/inverseDistance/inverseDistanceCellCellStencil.C
index 3f40b84503..ce5f1ef2d0 100644
--- a/src/overset/cellCellStencil/inverseDistance/inverseDistanceCellCellStencil.C
+++ b/src/overset/cellCellStencil/inverseDistance/inverseDistanceCellCellStencil.C
@@ -1552,9 +1552,11 @@ void Foam::cellCellStencils::inverseDistance::createStencil
             cellInterpolationMap().subMap(),
             false,
             samples,
+            greatPoint,                             // nullValue
             minMagSqrEqOp<point>(),
             flipOp(),                               // negateOp
-            greatPoint                              // nullValue
+            UPstream::msgType(),
+            cellInterpolationMap().comm()
         );
 
         // All the donor cells will now have a valid cell centre. Construct a
diff --git a/src/parallel/distributed/distributedTriSurfaceMesh/distributedTriSurfaceMesh.C b/src/parallel/distributed/distributedTriSurfaceMesh/distributedTriSurfaceMesh.C
index 293b5058cf..0f2ab38b60 100644
--- a/src/parallel/distributed/distributedTriSurfaceMesh/distributedTriSurfaceMesh.C
+++ b/src/parallel/distributed/distributedTriSurfaceMesh/distributedTriSurfaceMesh.C
@@ -1392,9 +1392,11 @@ void Foam::distributedTriSurfaceMesh::surfaceSide
         map.subMap(),
         map.subHasFlip(),
         volType,
+        zero,
         volumeCombineOp(),
         noOp(),           // no flipping
-        zero
+        UPstream::msgType(),
+        map.comm()
     );
 
     if (debug)
@@ -3193,9 +3195,11 @@ void Foam::distributedTriSurfaceMesh::findNearest
         map1.subMap(),
         map1.subHasFlip(),
         nearestInfo,
+        nearestZero,
         nearestEqOp(),
         noOp(),             // no flipping
-        nearestZero
+        UPstream::msgType(),
+        map1.comm()
     );
 
 
@@ -3351,9 +3355,11 @@ void Foam::distributedTriSurfaceMesh::findNearest
         map2.subMap(),
         map2.subHasFlip(),
         localBest,
+        nearestZero,
         nearestEqOp(),
         noOp(),             // no flipping
-        nearestZero
+        UPstream::msgType(),
+        map2.comm()
     );
 
     // Combine with nearestInfo
@@ -4183,9 +4189,11 @@ void Foam::distributedTriSurfaceMesh::getVolumeType
         map.subMap(),
         map.subHasFlip(),
         volType,
+        zero,
         volumeCombineOp(),
         noOp(),           // no flipping
-        zero
+        UPstream::msgType(),
+        map.comm()
     );
 
 
diff --git a/src/sampling/meshToMesh/meshToMesh.C b/src/sampling/meshToMesh/meshToMesh.C
index 3bb266dc6d..9601fe3d8b 100644
--- a/src/sampling/meshToMesh/meshToMesh.C
+++ b/src/sampling/meshToMesh/meshToMesh.C
@@ -556,9 +556,11 @@ void Foam::meshToMesh::calculate(const word& methodName, const bool normalise)
             map.subMap(),
             false,
             tgtToSrcCellAddr_,
+            labelList(),
             ListOps::appendEqOp<label>(),
             flipOp(),
-            labelList()
+            UPstream::msgType(),
+            map.comm()
         );
 
         // Set up as a reverse distribute
@@ -572,9 +574,11 @@ void Foam::meshToMesh::calculate(const word& methodName, const bool normalise)
             map.subMap(),
             false,
             tgtToSrcCellWght_,
+            scalarList(),
             ListOps::appendEqOp<scalar>(),
             flipOp(),
-            scalarList()
+            UPstream::msgType(),
+            map.comm()
         );
 
         // weights normalisation
diff --git a/src/thermophysicalModels/specie/thermo/thermo/thermoI.H b/src/thermophysicalModels/specie/thermo/thermo/thermoI.H
index c7a7c28abf..49e2e134a5 100644
--- a/src/thermophysicalModels/specie/thermo/thermo/thermoI.H
+++ b/src/thermophysicalModels/specie/thermo/thermo/thermoI.H
@@ -74,6 +74,11 @@ inline Foam::scalar Foam::species::thermo<Thermo, Type>::T
         {
             FatalErrorInFunction
                 << "Maximum number of iterations exceeded: " << maxIter_
+                << " when starting from T0:" << T0
+                << " old T:" << Test << " new T:" << Tnew
+                << " f:" << f
+                << " p:" << p
+                << " tol:" << Ttol
                 << abort(FatalError);
         }