Custom maps are 'geo referenced' maps and stored as .kmz files in the 'Custom map' folder of the GPS.


There are 'restrictions' on Custom mapping for a Garmin GPS

  • Map images over 1 megapixel in size (1024x1024 pixels, 512x2048 pixels..... in short, any image that contains more than 1048576 pixels) will be displayed at a reduced resolution on your GPS. In other words, fine map details and text will become indistinguishable. 
  • All map image files must be less than 3 MB 
  • Depending on your device you can upload no more than 100 or 500 custom map images or tiles. It doesn't matter if you have the storage space, any more and they won't load.
Instructions in how to create Custom Maps from the Garmin website are HERE

The Internet is awash with the same kind of instructions and other people's thoughts. 

The critical part of the process is the initial quality of the image, jpeg file. 

From a very good image on a digital OS mapping product for the UK it is possible to create a very good 'geo referenced map' image of about 28 square km (7km x 4km). The file size is 700kb and the quality is absolutely fine. Any area bigger than that and the quality, when the map is zoomed in, disappears and the map is unreadable. 

As already mentioned, the first step, the jpeg file of the map, has to be very good quality before it is 'overlayed' over Google Earth.

Once the Custom map has been created, the way to transfer them to your GPS is to open up the Garmin Internal Storage Folder>Custom Map folder and 'Copy' and Paste the kmz file directly in to it. 


If you wish to store the Custom Maps on your computer, then you can do so using Basecamp in the normal way as you do for transferring routes etc to and from the GPS.


Please do not use the map card, the storage device shown as a long number, when viewed on a computer.