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