Hi, Ive discussed with Frank if there might be a field in the tdb file that has to be changed. Maybe there is a value that tells MapSource something about the alignment of DEM data? I don't have a single original Garmin tdb file :-( It seems that mkgmap writes some constants that might be important, e.g. MapDetailBlock.java contains //01 c3 00 ff os.write4(0xff00c301); os.write(0); os.write(0); os.write(0); The wiki [1] describes these 7 bytes as "byte:0 has copyright text,byte 1: has 0x53 text : byte 2:if 1 then bytes 3_7: an unknown total (density) " The display tool seems to expect something similar to the wiki: d.rawValue(2, "01 01"); d.byteValue("intro flag"); d.intValue("intro %d"); Any idea what this "intro" or "unknown total(density) could be ? And what is the 0x53 text? [1]https://wiki.openstreetmap.org/wiki/OSM_Map_On_Garmin/TDB_File_Format Gerd