Todd Todd, GPS is a method to determine horizontal and vertical position of locations on Earth. It uses satellites that broadcast a signal and receivers that pick up and record the signal.
Hikers can use a hand-held GPS to find their position.
Farmers here in North Dakota use GPS to locate specific areas in their fields that need special attention. Volcanologist use GPS as a powerful tool to detect movement at shallow depths beneath the surface of volcanoes. With GPS, the velocity is the speed of light. The signal from the satellite includes the time it was sent. The receiver notes the time the signal arrived.