Hi WanMil, Mark, all, I analyzed all the multipolygon errors and warnings I got for today's finland.osm.bz2 from Geofabrik, without --generate-sea. Most of them can apparently be blamed on missing boundary information. I wrote the relation IDs an explanations to my logging.ignore file, so that I will not have to see these messages again. You can get the file from http://www.polkupyoraily.net/osm/, but I will repeat the interesting bits here: # overlapping lines in multipolygons, should be fixed in mkgmap later http://www.openstreetmap.org/browse/relation/48542 http://www.openstreetmap.org/browse/relation/367049 http://www.openstreetmap.org/browse/relation/372975 http://www.openstreetmap.org/browse/relation/387793 http://www.openstreetmap.org/browse/relation/389976 # multipolygon problem at tile border, should be fixed in mkgmap or splitter http://www.openstreetmap.org/browse/relation/302897 http://www.openstreetmap.org/browse/relation/306274 http://www.openstreetmap.org/browse/relation/311221 (the offending tile border is at lat=62.226562; the other one is at lat=64.819336) I could not see what is causing the following issues. WanMil, can you please analyze these? One of them was edited recently, but the other was not, as far as I can tell: 2010/01/29 12:11:44 WARNING (MultiPolygonRelation): 63240001.osm.gz: Multipolygon http://www.openstreetmap.org/browse/relation/372970 contains intersected or overlapping ways 2010/01/29 12:11:44 WARNING (MultiPolygonRelation): 63240001.osm.gz: Multipolygon http://www.openstreetmap.org/browse/relation/375636 contains intersected or overlapping ways Last but not least, here is an idea for quality control. I came across two lakes whose islands were in another lake (the change message hinted that the lake had been split). There is no warning for that. The errors must be coming from missing boundary information in the Geofabrik extract. http://www.openstreetmap.org/browse/relation/303320 http://www.openstreetmap.org/browse/relation/303321 Best regards, Marko