Not all the map files can be used on the memory card.
Here are some names used by Garmin OS:
- gmapsupp.img - maps you download, can be both internal and external on a SD card (this name is most common, and it means you can copy it into your GPS internal memory or memory card
- gmapprom.img - built in maps like City Navigator, only internal
- gmapprom1.img - built in extra maps, only internal. City Navigator EU and US need two files
- gmapbmap.img - base map file, can only be internal (on the GPS device)
- gmapoem.imb - OEM maps, only internally