yes, it is possible, but it depends on your gps model
So please tell the model / kind of your gps device and I / we can answer your question!
When using HomePort on your PC you can put many maps on one SD card and / or USB device and you will see them all.
In my Oregon 400 I'm using 8 GB SD cards with maybe 10 maps on it.
Some devices recognice only one map on SD card (named gmapsupp.img).
Look for answer to your question also [Only registered and activated users can see links. ]