In .System folder:
gmapbmap.img --> world basemap
gmaptz.img --> Time Zone map
gmapprom.img --> City Navigator map (ie Europe or America or Southeast Asia or Singapore/Malaysia or .....)

In Map folder:
xxxxxxxx.img
yyyyyyy.img
....
....
zzzzzzzz.img
In map folder you can use any name you like, there is no need to use the name gmapsupp
In map folder you can copy as many map files as you like (I use 8 maps)

In Streetpilot's map list you must have only one map (routable map) checked every time, but you can also check a DEM map (no routing data) or any other transparent map (like a topo transparent map with height contour lines, rivers, lakes etc and no routing data).