Last year, I posted about using the free command-line utility mkgmap to convert Open Street Map (.osm) data into the .img format used by Garmin GPS units, with a later post trying it out with US OSM data based on TIGER data. If you need to access any of the command-line options, you’ll need to use it in its original command-line format, but in many cases you’ll only need to tell mkgmap which osm file you want to convert, a fairly simple command. I created a simple GUI to simplify this for the command-line-allergic like me, but there’s now a better one available from Activity Workshop. It’s open-source (written in Java), checks to make sure you’re not overwriting another file (which mine doesn’t), and also lets you combine multiple .img files into a single file:
Hopefully some of the command-line options will be added to a future version.
Also available from Activity Workshop is a program called osmwrangler. OSM files often contain not just road data, but also locations for amenities like restaurants, parks, doctors, theaters, prisons, etc.; a full list is available here. These will be converted by mkgmap into points on the Garmin map, regardless of whether you want them or not. osmwrangler gives you the option of removing whichever amenity types you don’t want in your map, and generating a new OSM file without them that you can then run through mkgmap. Oddly enough, it’s only currently available in command-line format.