Global Positioning Systems

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Global Positioning Systems, commonly referred to as GPS, are a system of satellites and receivers that fix a location on the earth’s surface. It allows users to know their location and speed anywhere in the world. Although GPS is technically an entire system, in the common vernacular, GPS generally refers to the user segment of the system, which many people use for navigational purposes. [1]

GPS components

The components of GIS can be split into three segments: The space segment, the control segment, and the user segment. Each of these segments contains different instruments and functions which combine to make the system as a whole.

Space Segment

GPS satellite orbits around the earth

The space segment of the system is comprised of 27 satellites that orbit the earth. These satellites orbit the earth at about 12,550 miles (20,200 km) above the earth’s surface. [2] The satellites orbit on 6 different orbital planes, each of which crosses the equator at a 55 degree angle. Each plane has about 4 satellites along its path; this configuration allows enough satellites to be available at any time to calculate locations. The satellites send out radio signals, which continuously transmit data about the satellite’s position to receivers on the ground. As long as the receiver as able to receive the radio signals, it can compute the user’s location. This means that some areas make it difficult to calculate positions, interfere with signals, and increase error because of interference, such as heavy forest canopies, canyons, and skyscrapers. [3]

Control segment

GPS control stations around the world

The control segment consists of 28 ground stations throughout the world that monitor the satellites transmissions, track the satellites, and send commands to the satellites. The master control station is located in Colorado, while the alternate master control station is located in California. Both of these stations are in Air Force bases. In addition to these master control bases, 11 antennas and 15 monitoring sites make up the ground station controls. [4]

User Segment

The user segment of GPS are the receivers that use the data transmitted from the satellites to fix their location on the earth. These include everything from the everyday GPS that the average person buys for navigation to the ones used for military applications.

How GPS works

Global Positioning Systems calculate their position by measuring how long it takes for a radio signal from the satellite to reach the receiver on the ground, and uses that to calculate the distance from the satellite to the receiver. This is possible because the speed at which the signals travel and the position of each satellite are both known variables. Also, the GPS receivers and the satellites have clocks that are synchronized, so they can accurately compute the time it takes for the radio signals to travel to the earth’s surface. The GPS receivers gather all the timing and position data from three or more satellites. It’s through these multiple data points that the GPS can calculate locations. However, while technically a minimum of three satellites are needed to calculate position, a fourth satellite is needed in practice to correct for errors. [5]

Uses for GPS

GPS can be used for much more that navigating roadways, although that is usually the first thing people think of when they think about GPS. GPS can be used in farming to apply fertilizers and pesticides only where needed, to locate and map weed and disease locations are, and to guide aerial pesticide sprayers. It can be used in emergency response situations, search and rescue efforts, managing trucking services and public transportation, shipping fleets, and almost any navigational need. It can also be used for mapping natural resources and natural disaster damage. If something needs to be mapped or navigated through, then GPS is probably involved somewhere in the process. [6]

See also



  1. General Information On GPS. (n.d.). Retrieved May 29, 2016, from
  2. Space Segment. (n.d.). Retrieved May 29, 2016, from
  3. Understanding the Global Positioning System. (n.d.). Retrieved May 30, 2016, from
  4. Control Segment. (n.d.). Retrieved May 31, 2016, from
  5. Understanding the Global Positioning System. (n.d.). Retrieved May 30, 2016, from
  6. Understanding the Global Positioning System. (n.d.). Retrieved May 30, 2016, from

External links