Hi, based on some freely(?) available maps with DEM data and on "empty" DEM files created by GMapTool I started to analyze the DEM subfile format. With the little information I got so far (see http://wiki.openstreetmap.org/wiki/OSM_Map_On_Garmin/DEM_Subfile_Format) I managed to write some rudimentary code to create empty DEM files with mkgmap (just the same as GMapTool can do). If anybody has more information on the DEM format, I would be very happy to hear about it. Best wishes Christian