Using GMapTool to convert OSM Topo maps for Garmin

Looking to add open source maps to your Garmin GPS and trying to use the GMapTool?

This should help convert OpenStreetMaps downloaded from to a format usable by older Garmin GPS devices (.img) using Windows as the OS.

  1. Download GMapTool here:
  2. Install the GMapTool, put a shortcut on your desktop, and launch the program.
  3. Download map data here:
    1. For example, to use USA South Central TOPO map data, use this link for the map data page and the download link is at the bottom of the page.
  4. Using an unzip program (such as WinRAR), right-click on the .7z (7 zip) file and select “Extract to [folder name]“.
  5. Once extracted you’ll have another folder for your map region data. In this case “US_South_Central_OSM_Topo.gmap”.
  6. Open the folder and then open the sub folder labeled “Produc1”. Verify that you have many folders with numbers as the folder name. In our case we are back in “D:/Users/[username]/Downloads/US_South_Atlantic_OSM_Topo_v25a/US_South_Atlantic_OSM_Topo.gmap/Product1/” folder.
  7. Copy that folder path.
  8. Open GMapTool program. Select “Files” tab, select “Add Directories”. Paste the folder path in the “Filename” field. You should immediately see your many folders with numbers as folder names appear in the window.
  9. Click on the first folder, hold down shift, scroll to the bottom, and select your last folder. All folders should be highlighted.
  10. Click OK.
  11. Click the “Join” tab. Click “Output file”, select a directory, and add “gmapsupp.img” to the end of the directory.
    1. For example, mine is “D:/Users/[username[/Downloads/US_South_Atlantic_OSM_Topo_v25a/gmapsupp.img
    2. Give your mapset a name. I used gmapsupp.
  12. Click “Join all”.
    1. The program will now generate a gmapsupp.img file in the directory you chose.
  13. Connect your Garmin GPS in mass storage mode.
  14. Open your MicroSD card (via USB-connected Garmin GPS). Create a folder called “GARMIN” if it doesn’t exist.
  15. Open the “GARMIN” folder and copy/paste your gmapsupp.img file.
  16. If you need help changing your map use this tutorial:
  17. Once your map has been copied over, power off then power on your GPS. You will see a loading bar scroll across the bottom and, if your map has turn-by-turn navigation data you will also see a message about turn prompts.
    1. Drill down into your map settings using the tutorial from step 16. You should now see your map data folders. If you zoom out quite a bit you will also see your overlays for the region you selected.
  18. Enjoy your open source maps!



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