Q&A special: Satellite-Navigation - How does sat-nav work?

Q: How do satellite-navigation systems work?
B Lawton, Colchester

A: Satellite-navigation uses the Global Position System (GPS), a network of satellites which transmits signals to receiver equipment on the ground. At least 24 satellites are in operation around the world at any one time.

A sat-nav system in a car receives signals from several satellites at one time to triangulate a precise location. This information is combined with mapping information in the sat-nav system to establish the exact position of the car and calculate your route.