The Maplets app for iOS has different maps than any of the above: they scan free and public domain maps worldwide, most with GPS calibration. For example, you know those nice maps provided at the entrance to the US National Parks? They have scanned them all, and you can download and view them on your iOS device for planning purposes, then use them live when you're there. Many GPS maps, especially USGS topos, don't have accurate trails, but the trail maps available in Maplets are nearly always complete and correct. And not just hiking trail maps: subway maps, zoo maps, university maps, bike trail maps, municipal maps, airport maps, tourist info maps, ski area maps,...over 5000 maps, so far. They scan the complete map, including accompanying information (descriptions, campground details, schedules, etc.) You can also submit your own maps to their database, if what you want isn't already there. The app is $3.99; maps are free.