1. A method for determining a likely region for an object comprising: generating a set of calibration maps for an area by the steps of: transmitting a plurality of signals from a plurality of known transmitter locations; receiving said plurality of signals and measuring a difference between two properties for each of said signals of said plurality of signals, said receiving being from known receiver locations; and recording a plurality of calibration maps, each said calibration map relating one of said differences between two properties for each of said signals of said plurality of signals to corresponding locations within said area; transmitting a location signal; receiving said location signal and measuring a difference between two properties for said location signal; comparing said difference between two properties for said location signal with a corresponding said calibration map to generate a plurality of comparison maps; combining said plurality of said comparison maps to generate a combination map; and determining said likely region, said likely region being a region within said combination map defined by a predetermined threshold.