GPS Satellite System
Originally designed for the U.S. military, GPS technology uses satellites orbiting the Earth to pinpoint your location anywhere on Earth.
How GPS Works
According to REI, a GPS system uses signal from three or more satellites to locate your position on land or sea.
GPS systems are very accurate. REI says to expect a GPS system's accuracy to be within 20 to 30 feet. Some advanced systems have accuracy of 3 meters or less in ideal conditions.
Because a GPS unit requires satellites to get an accurate reading, obstacles such as tall buildings, high canyon walls and dense forests can block signal reception.
GPS systems should never replace a map and compass. GPS systems can run out of batteries, fail to get a signal or malfunction.