Hi Gerd A while ago, when I was trying to understand the multi-polygon code, one of the first things to strike me was that it seems to make things more complicated that they should be by not keeping the inner and outer ways parts separate during the initial processing in MultiPolygonRelation done by getSourceWays() and joinWays(). Instead, could have two instances (inner & outer) of a class that code like getSourceWays() can add() a way to, after choosing the correct class based on role/r_e.getKey(). The class holds unclosedWays, closedWays and the add() method will: 1/ test if already closed and add to closedWays & return 2/ test if either end joins to one or two elements in unclosedWays. if so, join in appropriate direction, remove second unclosedWay if joined both ends to different unclosedWays. if now closed, remove from unclosedWays and add to closedWays & return 3/ add to unclosedWays Another method to call at end to flag error for each unclosedWay Now the logic can proceed with working out which outers contain inners and start cutting... Feel free to ignore all of this. Regards Ticker