How to install topographic maps into Garmin Etrex 10

According to the manufacturer, Garmin eTrex 10 has a pre-installed world wide base map in it, and if you need more detailed maps, you should buy one of the more expensive Garmin models.

Yes, Garmin eTrex 10 has a world wide base map in it, and by using it you can easily find features such as continents and oceans, and, if you are seriously lost, the map shows you even smaller land marks, such as the Great lakes, New York city, and LA. “God damn it, I was sure I was approaching either the New york city or LA, but from my trusty Garmin map, I was able to see that the town in front of me was Chicago. Thank you Garmin!!”
Unfortunately, for most of the people who use hand held GPS devices, the knowledge whether the hill in front of them belongs to the Himalayans or to the Andes is not quite enough. Therefore, they have to buy an expensive GPS thingy and loads of maps to it.
Wrong! Although, the Garmin Etrex 10 does not have a slot for external memory cards, or any commercially available maps for it, it has some internal memory space for its own operational purposes, and for the storage of its useless world wide base map.
By replacing the original base map file with your own map file, you can load very, very detailed topographic maps to your Garmin eTrex 10.

First you need to find a map file covering the area of your interest. The requirements for the file are a) .img file format for Garmin devices, and b) size no larger than 8 MB (8MB is the available space after deleting the base map).

The internet is full of sources for right size .img map files, some areas covered better than the others. If you cannot find ready made files for your area, the net is also full of instructions how to chop and convert practically any kind of map files to the .img format.
I may, one day in the future, address the chopping and converting process, but in this entry, I’m only describing how to replace the base map with an existing .img file.

When you have downloaded the .img file, connect your Garmin eTrex 10 to your computer.
After a little while (eTrex is saving the track logs and such) you shall see either a Garmin logo on your screen, or a pop up window asking what to do. Either double click the Garmin logo or click the part that says: “view folders or files”.
In the following window, double click the Garmin folder.
In the next window, among the other files and folders, there is one named “gmapbmap.img” (that is the world wide base map file). If you want to save the base map, copy it first somewhere to your computer. Then right click the gmapbmap.img, and choose Delete.
Next, drag your own .img map file to the Garmin folder. (It may take couple of minutes to copy the file into your Garmin).
When the copying is done, right click your file in the Garmin folder, and choose Rename.
Rename your file to gmapbmap (this way your Garmin device is cheated to believe that the new file is a real Garmin map file.)

An optional way to install maps into your Garmin is to use Garmin’s own MapInstall program (freely available from The program recognizes your Garmin device and available maps in your computer. Then you can choose the map you want to be installed and let the program do the rest. However, you still need to rename the installed file before you can use it.

After these few simple clicks, your Garmin eTrex 10 should be ready for some serious navigation.
A limiting factor in a “maps for Garmin eTrex 10” project is the limited size of storage in the device, which requires computer access when ever you move to a new area. However, a very detailed 8 MB map covers about 1152 square kilometres (24X48) or 450 square miles (15X30), which, in most of the cases, is quite enough for an average hiker.

Well then, if these maps are so great, and easy to install, why don’t Garmin sell these maps to the consumers?

The answer is obvious: if these maps were readily available for an entry level <100 €/$ device, no one would buy those 200-300 €/$ thingies.

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