I currently use an excellent set of printed topographic route maps for mountain biking. I would like to scan the maps, georeference them, and upload the maps to a handheld GPS device.

Does the etrex series (10, 20, 30) support raster maps? Can I georeference the JPEG image using open source software?

4 Answers 4


For etrex 20 & 30 (but not the 10)

see the compare guide: https://buy.garmin.com/shop/compare.do?cID=145&compareProduct=87774&compareProduct=87771&compareProduct=87768 (see custom maps compatible)

Garmin have free instructions on how to use Google Earth and your custom images (scanned topographic route maps) in this case and loading it to the gps device.

Add the Image as Google Image Overlay

Reference the Image

Save as Places

Send Your Custom Map to Your Device

Connect your Garmin outdoor handheld device to your computer with a USB cable. In Google Earth on the left side of the screen, right click on your custom map. Click Save Place As.

In the dialog box that appears, find the drive for your connected handheld device and save³ your custom map in the /Garmin/CustomMaps/ directory (you may need to create a new "CustomMaps" directory if this directory does not exist). Save the file in KMZ format.

full instructions http://www.garmin.com/us/products/onthetrail/custommaps#fragment-2


Quantum GIS has a plugin "Garmin Custom Map" for the purpose you want: http://hub.qgis.org/projects/garmincustommap

You can get it via the standard python plugin repository. I have not tried it myself, because my own (old) Etrex can not read custom maps. Georeferencing is installed by default with Quantum GIS, and you can add selfmade vector overlays or GPX tracks too.

The size of Custom Maps is limited by Garmin, so you better start off with some smaller test cases.


One option is to use QlandKarte GT. This is free/open-source software, available for Windows, OS X, or Linux.

  • To reference the map, you can go to map menu -> Edit/create map. Then follow the steps convert the map into a GeoTIFF. Then create a map collection from that.
  • Go to map menu -> Select sub map, and select the tiles in your map.
  • Choose the selected map, then "Export map", and pick the option to export as "Garmin Custom Map"

This will export as a KMZ file, which you can copy onto the Etrex, in the Garmin\CustomMaps directory.


I posted a python script to use from ArcGIS here:

Exporting 3GB ArcGIS Raster to KML without losing resolution?

KML is uncompressed KMZ. The output here will work in either application. Georeferencing the scans could be done any number of ways; write a world file manually, use software. You can do it in Google Earth. But I feel the interface is very clunky and limited.

The different models support different numbers of tiles. You have to look at this limitation, the extent of imagery you want to use, and the minimum resolution you want to use. Then you need to possibly create multiple files from your original imagery, process each section of imagery with the script tool, and transfer the files from a laptop to the GPS as you need them (Garmin only supports one "Custom Map" at a time). Many of the *map models only support 100 1024x1024 tiles. The Colorado and Montana support more. I experimented with changing the tile size to 2048 x 2048 and that seemed to still work and allow for quite a bit more data at a time.

  • 1
    Note this solution (and your script) requires ArcGIS, which is not open-source software as the original question requests.
    – Chris W
    Apr 30, 2015 at 20:20
  • Man.... You guys really want to fight me on giving something away.... I see no mention of open source... OK Map would be the closest...although it is free use not open source I don't think. Seem to remember a nag screen. This would play well into the georeferencing of scans, but if you are going to pay for large format color scans.... You should reference them accurately.
    – Mike
    Apr 30, 2015 at 23:07
  • It's the last line of the question: "Can I georeference the JPEG image using open source software?" The other question where you actually posted the script (and we do appreciate that kind of sharing) is specific to ArcGIS. And as another answer mentions, QGIS is free/open-source and can do georeferencing. I'm not sure how that might compare to OK Map.
    – Chris W
    Apr 30, 2015 at 23:17
  • Your right....I can't read. I haven't ever used Quantum for this either, but I have used OK map, and it forces you to define extents when you import your (unreferenced) image.
    – Mike
    May 1, 2015 at 1:20

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