The Global Positioning System (GPS) enables a traveller to find out his or her position anywhere on or above the planet. In order to use the GPS, a user buys a locator which can calculate distance by measuring the time it takes for the satellite's radio transmissions, travelling at the speed of light, to reach the receiver. Once the distance from four satellites is known, the position in three dimensions (latitude, longitude, and altitude) can be calculated using mathematical calculations called trigonometry. Velocity in three dimensions can be computed from the principle of doppler effect in the received signal. Of course, the new GPS receivers do all the work for the users. The mathematics are pre-programmed into the locators, and the information is displayed automatically.

GPS technology has applications other than determining a position on the Earth. One innovative application of GPS technology is to determine the Earth's movement after an earthquake. By consulting a network of these sensitive receivers, you can make remarkably accurate measurements of the movement of the Earth's crust. GPS was also used to locate precisely drop points for airlifted Bosnian relief supplies. GPS has also accomplished pure data collection for use in the scientific community. GPS is addressing such problems as volcanic processes, ice dynamics, sea level change, and atmospheric sounding.

The GPS is made up of three segments: space, control, and user. The space segment consists of the network of satellites orbiting the Earth. The control segment is made up of monitor stations on the Earth, which track the satellites in view, accumulating data and updating each satellite's navigation message. Updated information is transmitted to each satellite via ground antennas. The user segment consists of antennas and receiver-processors that provide positioning, velocity, and precise timing to the user.