GPS is an acronym for Global Positioning System. GPS is a network of satellites and receivers that communicate for navigational purposes. GPS satellites are used to create maps, survey land and determine distance, velocity and coordinates.
The process used to calculate the exact coordinates of a receiver is called three-dimensional trilateration. Each receiver has a quartz clock inside, and each satellite is equipped with an atomic clock. Distance is measured by calculating the amount of time it takes for a signal to travel from a receiver to a satellite. By measuring the distance of the receiver from three or four satellites, the coordinates of a receiver on Earth can be pinpointed within a few meters of exact location.
GPS receivers are available commercially for automobile drivers. Receivers are sold preprogrammed with road maps and detailed traffic information, such as speed limits, street names, flow of traffic and parking lot locations. By synthesizing the coordinates from the satellites and the preprogrammed maps, GPS receivers can tell a driver what roads to travel, where and when to turn and the travel time needed to reach a desired location. For most GPS receivers, maps are updated once a year via an upload provided by the navigation system manufacturer. Usually additional uploads and features, like maps of foreign countries, are available for a fee.
To use a GPS receiver, a driver must enter a destination address into the navigation device. The GPS receiver will wait for a signal from a satellite and then calculate the route of travel. Many GPS devices will include features that grant the driver some control over the route the GPS device chooses to display. For example, a driver can avoid highways, interstates or U-turns.
GPS maps are frequently programmed with information that can tell a user the nature of the businesses in his current location, along his travel route or near his destination. This allows a driver to search for specific businesses (such as restaurants and gas stations) while en route.
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