Hi Gerd This might have nothing to do with the issue but I've been curious why all basemaps ( in the past) & now overview maps cause Mapsource & Basecamp to crash when the tdb lock byte is set. This interestingly does not happen when cgpsmapper is used to create the basemap . One of the differences seems to be that the latter includes a 0x4b polygon to define the outline.(+ Background=Y) Am I correct that the main outline / frame (4b polygon) is not defined as such but presumably calculated by Mapsource? This might lead to unwanted effects? BW the overview maps work really well with reduced map windows. .. Nick -- View this message in context: http://gis.19327.n5.nabble.com/polygon-type-0x4a-tp5761430p5763111.html Sent from the Mkgmap Development mailing list archive at Nabble.com.