Mark_S
7
As the other post says a gmapsupp.img file is a container file that can contain lots of individual maps. The gmapsupp.img file is not really a map itself.
There are programs around that will manipulate these gmapsupp.img files. I often use one call gmaptool (http://www.anpo.republika.pl/download.html). This can extract the individual map files from a gmapsupp.img file or combine multiple gmapsupp.img files (or individual maps) to create a new gmapsupp.img file. If you use it to combine your individual gmapsupp.img files then you can just put the combined gmapsupp.img file on the SD card.
Mapsource can also create a combined gmapsupp.img file, but seems to require the individual maps and things like an overview map (which is effectively a map of the individual maps) to work. You can create these from the contents of a gmapsupp.img file but it always seems hard work to me.