Garmin GPS

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Not only can the GPS unit be used to gather data for Openstreetmap, but the result can be viewed afterwards on the GPS! However the raw '.osm' data is not directly suitable for upload to the Garmin GPS unit. Because the processing power of a small unit can under no circumstances compete with the fast servers on the internet, each GPS manufacturer has defined their own smart formats to quickly access the map data.

Garmin, one of the first producers of GPS devices with maps, has defined two of such formats. With the evolution of the GPS devices more and more data needed to be present in the maps. Think of maximum allowed speed, lane information etc.. As such the initial Garmin format did not do it anymore and the NT format was born.

None of the Garmin formats have been published, however due to years of reverse engineering, the initial format is as good as complete. Several project on the internet have been initiated that have resulted in one of the most active communities in map making, giving a Garmin GPS owner the unique possibility to download several free maps.

Since it is only the initial Garmin format that is known, not all map features present in Openstreetmap can be mapped, but all in all, most of the results are quite amazing!

OSM Maps on your Garmin Unit

You don't have to be a wizzkid to get the OSM maps on your Garmin Unit. The process of converting the OSM data to the Garmin format has already been done for you! The list of available distributions can be found here. Note that most of the distributions are updated frequently ensuring that you have the most recent OSM data on your Garmin unit.

The Garmin unit is shipped with software to transfer maps to the GPS unit. This software application is called MapSource. Like any Garmin map distribution, most of the OSM distributions can be integrated into the MapSource application, making the process of selecting and transferring maps to the unit as easy as any other distribution for which you have to pay.

Note that the list of OSM distributions indicates whether a MapSource installer is available. If you are not one of those wizzkids, select a distribution with an installer. Once installation is finished, restart MapSource. You can select the OSM distribution on the left top corner of MapSource.

Note that many of the OSM distributions support routing. If your Garmin unit has the ability to guide you from point A to point B, select one of the distributions with routing capabilities.

Garmin Maps Explained

Like paper maps, a country or region is split into several smaller maps. All Garmin maps have the extension '.img'.

Before these maps can be used on the GPS unit, the maps have to be bundled in a single container. Usually, Garmin own software MapSource bundles the maps and stores it in the Garmin folder of the unit's memory.

Garmin supports the following container files:

  • gmapbmap.img Typically this is the preloaded base map.
  • gmapprom.img Typically this contains the preloaded detailed maps.
  • gmapsupp.img Typically the maps uploaded by Garmin MapSource.

Not all units support the same container files. To find out if your GPS unit supports these, just rename one and see if the maps are still visible. For some models the latest firmware upgrade removes the naming restrictions of the container files.

Each map has a unique 8 digit number identifying it and mapsets can be identified by their family id.

Individual maps cannot be viewed or selected directly from MapSource. For this a mapset has to be defined. Some of the free maps provide an installer that directly installs the map into MapSource. If such an installer is not available, the tool MapSetToolkit can be used to create the mandatory files for MapSource.

As an alternative to Mapsource, sendmap, mapupload or QLandkarte can be used to add single files into one aggregated file.

Changing Looks on your Unit

The maps of the OSM distributions contain a lot of data, sometimes cluttering the screen. Note that it is possible to define how and which of the data is shown on the screen. Many of the distributions include a .TYP file. This file can be edited using Just replace the .TYP file on your hard disk and the next time you transfer maps to the unit, the changes will be visible.

Some of the distributions use these .TYP files creatively to 'fix' the shortcomings of the initial Garmin format. Less interesting items of the initial Garmin format are used for things that had not been defined. The .TYP files are then used to render the items according to its new purpose. Similar tricks are applied by the distribution, showing all kinds of additional information about cycling tracks on the screen of your GPS unit!


Category:Garmin Gives an overview of all pages related to Garmin.

OSM Map On Garmin explains the process of transforming the maps into the Garmin format.

OSM Map On Garmin/Download provides a list of free to download Garmin maps.

Garmin lists the different Garmin units

OSM Map On Garmin/POI explains how Point Of Interest can be uploaded.

OSM Map On Garmin/Mass Storage Mode

OSM Map On Garmin/Cycle map Explains how graphics can be optimized to make maps more suitable for cycling.

OSM Map On MapSourceExplains how to view your map in MapSource