Garmin datacards and other data storage cards such as SD cards can transfer all MapSource data types. Note Each time you transfer maps to a data card, you erase all data stored on the card and replace it with new data. However, transferring waypoints, routes or tracks will not erase the maps on the card..There are other free maps for your Garmin GPS, and again, they might have different instructions for installation. Check the website where the maps are offered for directions on how to install them. GPSFileDepot is a great resource that’s frequently updated..Free topo and trail maps for your Garmin GPS. By Rich Owings Comments. If you’re a Garmin owner and aren’t aware of all the free maps available for your unit, you’re in for a treat. Detailed , scale topo maps are available for most states in the US, as well as for some foreign countries..Building on the success of more than years of USGS topographic mapping, the US Topo series is a new generation of maps of the American landscape. US Topo topographic maps are produced by the National Geospatial Program of the U.S. Geological Survey USGS . The project was launched in late , and the term “US Topo” refers specifically to quadrangle topographic maps.