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