OSM Map On Garmin/Format

From OpenStreetMap

Garmin uses an undocumented file format for its map files. The format has been partially reverse engineered, but there are still some unknowns. Garmin map files use the suffix .img.

Storage on Garmin devices

Newer Garmin GPS devices support mass storage mode, where the device pretends to be a normal storage device like an USB stick. To enable mass storage mode find the "Interface" setting in the config menu. On this storage device, you need a top level directory called Garmin and in it there is a single file called GMAPSUPP.IMG. This file can be created with the sendmap or QLandkarte programs.

File format documenation

To understand the Garmin map file format the best place to start is the Sourceforge project at [1]. Mkgmap comes with some code for disassembling and viewing Garmin maps: http://svn.parabola.me.uk/display; there's information on the mostly-understood routing network at http://svn.parabola.me.uk/display/trunk/doc/nod.txt. Libgarmin also contains more info on the format -- its aim is to read Garmin maps for routing in Navit.