GPS: finding a place with satellites — Technology, 7–10 years
GPS helps a device estimate where it is by timing signals from satellites in space. It can guide a journey, but it is measuring a position, not magically seeing the road ahead.
A position from timed signals
GPS means a receiver listens to signals from satellites whose positions are known. Each signal carries the time it was sent. By comparing arrival times from several satellites, the receiver calculates a likely spot on Earth.
Why know where you are
People once had to read maps, follow signs or ask for directions, which can be difficult in an unfamiliar place. Satellite navigation was developed to provide a position and help plan routes. A map app then combines that position with roads and other information.
A walk to the library
A phone receives signals from four satellites. The timing suggests it is near Park Street, and its map has the library 300 metres east. The phone draws a route from the calculated position to the library. It updates the position as the walker moves.
A map is not a camera
It is easy to think GPS knows every detail of a journey because a map app gives spoken directions. In fact, GPS mainly supplies position; maps provide roads, and traffic services provide delays. A wrong map, weak signal or blocked road can still lead to a poor route.
More than directions
GPS helps hikers check a trail, ships and planes keep to routes, and emergency teams find a reported location. Farmers can guide machines across fields, while sports watches record distance. Devices should not be treated as perfect, especially near tall buildings or indoors.
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