The map I generate of Iceland with mkgmap and --genarate-sea and --remove-short-arcs got flooded between 25th ond 26th October. If I just use the --generate-sea option the map is not --remove-short-arcs I get a lot of RoadNetwork warnings but the map is not flooded. Here are the two .osm files: http://osm.nix.is/archive/2009-10-25/Iceland.osm.bz2 http://osm.nix.is/archive/2009-10-26/Iceland.osm.bz2 Generated .img files: http://osm.nix.is/archive/2009-10-25/default/13314531.img http://osm.nix.is/archive/2009-10-26/default/13314531.img osmdiff report between the two: http://osm.nix.is/diff/archive/2009-10-26/01-day.html http://osm.nix.is/diff/archive/2009-10-26/01-day.png To reproduce this on the latest file just do: wget http://osm.nix.is/latest/Iceland.osm.bz2 bzip2 -d Iceland.osm.bz2 # Generates flooded map mkgmap --generate-sea --remove-short-arcs Iceland.osm # Map is not flooded mkgmap --generate-sea Iceland.osm