- Download the map image in compressed format from http://www.osmmaps.com/united-states.html. The file (usa_osm_29022012_gmapsupp.zip) that I downloaded on 30 March 2012 was 2.47GB.
- Expand the file to gmapsupp.img. Size is 3.31GB.
- Copy the image file to the Garmin micro SD card under the "garmin" folder. Note:
- My Edge 705 only supports one map image file that must have the name gmapsupp.img. Other units may support multiple files that can have different names. If you are not sure, then keep this one name.
- It takes about an hour to copy the file when the micro SD is inserted into the computer, using an adapter. It takes several hours when copying to the GPS unit using USB cable.
In general, to be safe, I use the GPX Track option from RideWithGPS.com (\garmin\gpx folder), and save the TCX course file as backup (\garmin\courses folder). Both options contain breadcrumbs of the mapped route. This is safer for two reasons:
- Follow the same exact route as it was mapped on the web site. There is less risk of the GPS unit calculating its own route that may be different from the intended one.
- Maintains the directions and route even when the road happens to be missing from the map, or when the route is on a trail that is not on the map. In fact, with a TCX file from RideWithGPS.com, even without a map, I still get the cue sheet prompts at turns.
The following web site allows for building custom images from selected map sections: http://garmin.openstreetmap.nl/
Plenty of instructions are at http://wiki.openstreetmap.org/wiki/OSM_Map_On_Garmin/Download
I am still experimenting with maps and languages outside the US. I loaded Japan's map and tested a few routes:
- The text does not display properly. Kanji characters are replaced with commas and periods. Road numbers and other Roman characters do appear.
- Small roads outside major metropolitan areas seem missing from Open Street Map, even on the web site. Probably will be added in time.
I found an old discussion on this forum circa 2008 at http://www.adventurecycling.org/forums/index.php?topic=4521
There is an active discussion on this topic at http://www.bikeforums.net/showthread.php/801939
I will post more results as I learn more. Pleas share your experience as well.