{HEAD ~ a positioning system} that determines {TAIL ~ a current location} relative to the data representing a geographic region; and 
determines
{ HEAD ~ a positioning system } that determines { TAIL ~ a current location } relative to the data representing a geographic region ; and
HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH