After playing around some more I think I found the reason for the problem. It appears that there is a conflict between the --min-size-polygon= parameter and sea generation from the precompiled files. For larger Values of --min-size-polygon, the tearracing becomes worse. For smaller values it becomes better. It seems that the generated sea polygons are filtered one at a time by --min-size-polygon. Which is probably a bug. With the default setting for --generate-sea or an explicit --generate-sea=multipolygon, the sea is supposed to be generated as a multipolygon. It does not make sense to filter out individual parts of a multipolygon. Multipolygons on land are treated as a whole, and the same should be true for generated sea polys. But it looks like the --precomp-sea option creates many individual sea polygons, not a multipolygon as described in the documentation. I think the simple solution would be to not apply the --min-size-polygon filter to generated sea at all. A coastline multipolygon usually extends over large parts of the map, so it would be never filtered. -- View this message in context: http://gis.19327.n8.nabble.com/Terraced-pixellated-coastline-with-precomp-se... Sent from the Mkgmap Development mailing list archive at Nabble.com.