Begun by the Air Force back in the 1970s, the GPS network now in use had a long gestation period, finally entering service in the 1990s. GPS navigation caught on with the motoring public in the early 2000s, as automakers incorporated the feature as a factory option and inexpensive dashboard-mounted devices such as Garmin and TomTom units became ubiquitous — before being largely replaced by smartphone navigation.
How Does GPS Work?
Spaced evenly over six different orbits at an altitude of approximately 12,550 miles, the GPS satellites circle the globe twice a day. This arrangement ensures that at least four are always visible to any given GPS receiver from any point on Earth, though geography and urban canyons formed by tall buildings can block these line-of-sight signals.
By combining the coordinates of any three satellites, the GPS receiver in your phone or car can fix its location. Adding a fourth satellite signal enables altitude to be added to the mix. By overlaying that information on top of a built-in or cloud-sourced map database, the receiver can provide the turn-by-turn directions drivers have come to rely on, along with the location of services like restaurants, gas stations and other points of interest.