Have a look at this site Topo.com and get the real scoop

Magellan Triton Series GPS receivers have become the first in the market to load TOPO! maps, not just routes and waypoints. In early 2008 the Maps division launched this site and the new TOPO! Explorer application, which enables users to not only create custom maps for outdoor recreation, but also to publish maps to our online community, discover recommendations of new places to go, and utilize a new nationwide set of topographic maps and aerial photography. http://ping.fm/L64bY