Hi David, my polygon for splitter is this: Ireland 1 -5.243715 51.323391 -10.915155 51.323391 -10.915155 55.476919 -5.243715 55.476919 -5.243715 51.323391 END END The advantage is that it is rectangular and therefore splitter will create a set of tiles which form a rectangular area, thus there is no need to use --dem-poly. I think this works well In combination with --precomp-sea option. I've never seen a hgt file that contains only 0x8000 values (voids), nore one that contains only 0x0000. Did you create that N56W008 with a tool? If so, why? Gerd ________________________________________ Von: mkgmap-dev <mkgmap-dev-bounces@lists.mkgmap.org.uk> im Auftrag von David <david.tlp@orange.fr> Gesendet: Donnerstag, 22. Februar 2018 19:26:48 An: mkgmap-dev@lists.mkgmap.org.uk Betreff: [mkgmap-dev] Rép : DEM test & artifacts Hello Gerd, I was not able to download your polygon file but it is not a problem. My own polygon works like a charm and it is absolutely not a rectangular shape. It is contained in the area where there is no shadow applied on water surface. Is there a difference between a tile full of nan values like N56W008 and when the tile does not exist mkgmap writes a message about using 0m for elevation by default ? Ireland -9.0 55.5 -6.0 55.5 -5.25 54.6 -5.25 54.0 -5.75 54.0 -5.75 51.5 -8.0 51.5 -8.0 51.25 -10.75 51.25 -10.75 54.6 -9.0 54.6 -9.0 55.5 END END All the best, David _______________________________________________ mkgmap-dev mailing list mkgmap-dev@lists.mkgmap.org.uk http://www.mkgmap.org.uk/mailman/listinfo/mkgmap-dev