I got the information below from the Explorist manual. The text reads like nstructions for verifying that the maps are loaded into the GPS. But how do you use/view the loaded maps? In my case I loaded some maps from a Magellan National Geographic Topo! subscription.

UPDATE: I figured it out - thanks anyway.

Maps
Additional maps for the eXplorist may be available
from the Magellan Store at http://www.magellangps.com.
Once the map has been purchased and installed you
will need activate it in your receiver.

Accessing Loaded Maps
1. Tap the Map screen to bring up the Four
Corner Menu screen.
2. Tap on the Main Menu icon in the lower left
corner.
3. Select Maps.
4. Choose World Maps or Detailed Maps to see
the individual maps installed.
5. If the map has a checkmark before its name
it has been activated and is in use by your
receiver. You can toggle the map on or off by
tapping on the check mark box to the left of the
map name.
6. Tap on the map name to get more detailed
information about the map that is installed.