I have installed a North America map and a Japan map on my HTC HD2 mobile phone. The NA map is called gmapsupp.img since it was the first map I installed. Later i installed the Japan map and just called it Japan.img since I did not want to use it until I got to Japan. When I went to Settings/Manage My data/My Maps I was surprised to see the Japan map listed. I can also select it. So I guess the Garmin app just looks for files of type img.