One very important use of GPS is to send time signals that allow clocks to be calibrated to within 200 ns (200 billionth of a second). Why would you need to know the time this accurately? Businesses that use computers in many parts of the world can synchronize their computers so that the precise time that transactions occurred are known.

GPS also provides navigation information. Hikers use GPS to replace maps, which are often outdated, compasses, and lists of landmarks. Automobile and truck drivers use GPS to replace paper maps and to find local businesses, such as banks, restaurants, and gas stations. Farmers use GPS to map precise locations in their fields. Not only does this information improve planting, it can be used to mark the locations of areas that need additional insect control chemicals or fertilizers.

Engineers are now working on GPS systems to improve the flow of automobile traffic and reduce crashes. Each car would have a GPS receiver that would then broadcast its position. This information could be used to change red traffic lights to green if there were no opposing traffic. If two cars were equipped this way, the system could determine the distance between them and their relative speeds. If they were on a collision course the system would apply the brakes to avoid a crash.