There are various standard filenames on the Nuvi...
gmapprom.img - pre-installed City Navigator map
gmapbmap.img - basemap (a crude map of the whole world)
gmaptz.img - timezone map, used to calculate arrival times across different zones
gmapdem.img - 3d terrain (Nuvi 3xxx series)
gmap3d.img - 3d buildings (Nuvi 7x5 and 3xxx series)
gmapsupp.img - user-installed supplemental map
As I said, you can use any name on the newer models, but yours is an old model. Any other names are model-specific on the Nuvi and I don't know which yours might support.
If you just learn how to install the maps in Mapsource, that will solve the problem since you can send multiple maps in a single gmapsupp.img file. Also helpful to be able to view it on your computer.
