First, let me introduce myself to the list. I'm new to geosystems, but learning quickly after I acquired a GPS receiver two weeks ago. I've written a makefile to turn SRTM elevation data into vector contour maps (I'll write it up on OpenStreetMap.org once I'm happy with it). One of the problems[1] I've had is that mkgmap exits with return code 0 always, even on failure. This means that the makefile blindly continues to make its dependents, with a missing or invalid .img file - or in the worst case, an old, out-of-date one. If you were to add System.exit(1) in appropriate places (probably just the exception handler in main()?) - I'd be really grateful, and so probably would others. [1] The biggest problem I had was with re-referencing the EGM96 data to OSGM02 - until I realised that the difference is well within the 1-metre precision of the source data, never mind its accuracy! BTW, does mkgmap dislike negative ID values when reading OSM files? gpsbabel writes these when writing, and I was wondering whether that's what was causing empty tiles in my first attempt.