Aspects of the present disclosure relate generally to indoor localization, for example, where GPS or other localization signals are unavailable. More specifically, aspects relate to using a particle filter in conjunction with a gyroscope and/or accelerometer to identify a current location of a client device with respect to a map. In one example, the map may be based upon a map including a series of walls representing locations where a user may not walk within a building. In another example, the map may be based upon a series of rails representing locations where a user may walk within a building.