GPS, or Global Positioning System, is a system for locating exact positions on Earth’s surface. It was originally developed by the U.S. military to help soldiers locate their positions on battlefields. The system is now widely used throughout the world. GPS is based on a network of more than two dozen satellites that constantly orbit Earth. A  GPS receiver on the surface uses information from the satellites to determine is own position. The receiver detects radio signals from at least four nearby GPS satellites. There are precise clocks on each satellite and in the receiver.     The receiver... Show more

GPS, or Global Positioning System, is a system for locating exact positions on Earth’s surface. It was originally developed by the U.S. military to help soldiers locate their positions on battlefields. The system is now widely used throughout the world. GPS is based on a network of more than two dozen satellites that constantly orbit Earth. A  GPS receiver on the surface uses information from the satellites to determine is own position. The receiver detects radio signals from at least four nearby GPS satellites. There are precise clocks on each satellite and in the receiver.    
The receiver measures the time it takes for the radio signals from each satellite to reach it. It uses these times, together with the constant speed of radio waves, to calculate its distance from each satellite. Then the receiver uses the four distances to triangulate its exact location on Earth’s surface.    
A related technology is Geographic Information Systems, or GIS. GIS uses exact geographic locations from GPS receivers, along with any type of spatial information, to create maps and images. The spatial information might be numbers of people, types of plants or soils, presence of groundwater, or levels of rainfall. Geologists use GIS to make maps of natural resource distributions, among many other uses.    

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