This post will guide you how to get routable OpenStreetMap(OSM) maps into your Garmin eTrex 20 GPS unit. OSM maps are not comprehensive compare to other Garmin maps that you can purchase from Garmin but never the less they are free and you have the whole world to select for download.
Note: I have tested this on my Garmin eTrex 20 and i am sure that this method also works for Garmin eTrex 30 units as well.
Before you start, download mkgmap and make sure you have java installed into your system because mkgmap is a java based command program.
- Goto Free routable maps for Garmin GPS devices and download the Garmin map (IMG format) of the region you need.
- Using mkgmap, give a description ID to your map so that you can identify the map from your Garmin eTrex 20 GPS device. You can disable it if you want to. The command is:
java -Xmx512m -enableassertions -jar mkgmap.jar --draw-priority=10000 --transparent --gmapsupp --description=<your map name> <downloaded map file>.img
- mkgmap.jar will create a new file, gmapsupp.img. Rename this file to your choice and copy the file into your Garmin eTrex 20 GPS unit.
Note: Garmin eTrex 20 is able to support multiple IMG files with different filenames. From the Map setup in the device the name of the IMG file is reflected from the description ID set in step 2.