The use of two known coordinates to determine the location of a third. Used by ship captains for centuries to navigate on the high seas, a form of triangulation known as "trilateration" is employed in GPS receivers to pinpoint their current location on earth. Trilateration is also used by cellular phone carriers to identify a caller's location for emergency 911 services.
Triangulation vs. Trilateration
Tri-ang-ulation deals with the measurement of the angle of the triangle formed between the observer and two known locations. Tri-lat-eration deals with the distances between observer and locations and is closer to what GPS navigation systems actually do. GPS uses three and four known locations from satellites to pinpoint the person or vehicle. See GPS