If you check out SLAM positioning, you can do some really amazing stuff even if all you know is how far away from the wall you are. Given a decent floor plan, y

If you check out SLAM positioning, you can do some really amazing stuff even if all you know is how far away from the wall you are. Given a decent floor plan, you simply take frequent distance measurements as you wander around, using dead reckoning (the accelerometer will help) to keep track of your relative positions. You rapidly build up a local map of the walls near you, which eventually will map uniquely to one location on the floor plan. Our robot only had to wander for a few seconds to figure out where it was, and that was just using a few ultrasonic rangefinders. I haven't heard of such a thing, but I imagine you could do something similarly cool with the camera of your phone. Or, even the accelerometer and compass, combined with a knowledge of the locations of doors and the available walking paths, may be able to give a reasonably good approximation of your current location--if you walked north for 30 meters, then turned left and walked another 20 meters, then north for an additional 5, in a typical mall that's going to limit the number of points you could be occupying.