Hi Ticker, sorry, I can't follow. The old code only preserved points on the boundary of the merged shape, but the outer ring can be far from rectangular. This way some important points on outer ring were not preserved. There's still a possible problem with large white area in sea which seems to depend on the order in which shapes are merged. Sill trying to understand what goes, but at least I can reproduce it... Gerd ________________________________________ Von: mkgmap-dev <mkgmap-dev-bounces@lists.mkgmap.org.uk> im Auftrag von Ticker Berkin <rwb-mkgmap@jagit.co.uk> Gesendet: Montag, 24. Mai 2021 17:11 An: Development list for mkgmap Betreff: Re: [mkgmap-dev] Problems with sea in overview map Hi Gerd Re. last commit: preserve all horizontal and vertical lines in shapes. Do the cut lines go right across the outer polygon or just in from one side to the hole? If all the way across, might this change inhibit the merging to one side of the hole, or, if divided for some other reason in the other direction, merging across the now unneeded cut line. Ticker _______________________________________________ mkgmap-dev mailing list mkgmap-dev@lists.mkgmap.org.uk https://www.mkgmap.org.uk/mailman/listinfo/mkgmap-dev