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