National Geographic are using the Google Maps API to display their own custom map tiles. Using the Google Maps API enables National Geographic to present a seamless interface for their excellent topographic maps of the entire USA and for their social sharing network of uploaded trails.
National Geographic's TOPO! Maps include satellite views, shaded relief maps, and hybrid maps, combining the satellite view with geographical information. Registered users of the site can explore the 1,989 trips, 1,090,850 miles of trails, 191,715 waypoints and 1,282 photos uploaded to the site by other users. They can also upload their own trails, photos and videos.