thread time spent in the general location,
how much you moved about? any flat is going to be smaller than the floorplan of a supermarket. however, visiting a friend that lives over a corner shop would be harder to differentiate
permalink I guess it they are working on bluetooth like the
apple one it's probably easier... but that doesn't track geographical data so less useful to pick up problem locations.

block of flats would seem a problem for anything that relies on GPS.