I just used the verify maps function of gpsmapedit (a new version was released a few days ago, that improved the error checking possibilities -- http://www.geopainting.com/en/ ) to check for errors in mkgmap created maps. Most found stuff is IMHO not really important. However there should never be the case that a routable line intersects itself. Of course this is a data fault in OSM, but maybe such intersecting lines harm the routing over longer distances... Usually the reported problems are roundabouts (but not tagged as such) - and no problem, sometimes there are really strange shapes however, or obvious errors like this (note the oneway arrows, that go against each other): There are also sometimes real intersections without roundabouts - those are really really rare however (found one, but then gpsmapedit crashed before I could make a screenshot, would need to search again to find em). Also sometimes gpsmapedit complains about too short distance (under 2.3m) of routing nodes, but I think these are false positives, as I think this problem got fixed after a report by me about 1 1/2 years ago. Not sure what to make of the other errors found. I think most are not really harmful - but just to list them. Other bugs that should be fixed but are not high importance to what I would guess: -- No space at the end of a string. (pretty rare) -- Polygons intersect themselves (again error in osm data, but cutting intersecting polygons into seperate single ones would be cleaner - or drop them altogether as obviously data is wrong) - this is quite common. --- Polygons have jitter - Polygons that have parts that get averaged to a straight line or that are a strait line in OSM data. Obviously those jitter points should be dropped.