Hi.
It is possible to have multi images on a micro sdhc card in garmin gps.
On a kingston Micro sdhc 8 Gb class 10 i have 12 different images on the card in my Astro 320.
name them: gmapsupp1-gapsupp2-gmapsupp3-gmapsup4 osv.
Aktivate the maps you need, and let the other be deactivated.

Regards
Asro