Zeb writes: "There are lots of printed maps out there with data that Google Maps doesn't have. For example: hiking trails and ski trails, public transit in some cities, and special information like a zoo map or a museum map. What I would like is to take a photo of such a map with my iPhone, supply my current location by tapping on the map, and enter the scale and orientation of the map — and then see my live position on the map as I move around, using GPS. The math behind this transformation would be very simple; I suspect the only complexity would be perspective-correcting the photo of the map. I have seen many apps that allow you to trace your route on Google Maps or some other pre-existing map, but none that allow importing a photograph of an arbitrary map. Does anyone know if this exists?"