"The term 'GPS' refers to any Global Positioning System. A GPS is a constellation of satellites orbiting the earth, transmitting precisely timed impulses which can be detected by a ground receiver. By comparing the tiny delays in the timing signals, the position of the receiver relative to the satellites can be calculated." This report looks at the various cases in which GPS could be used in law enforcement operations and procedures, as well as previous incidents such as those in Australia featuring Chinese traffickers.
National Law Enforcement Corrections Technology Center: http://www.nletc.org/