Consider for a moment that when you are traveling in a commercial airliner, the pilot and crew are navigating to your destination with the aid of data from the Global Navigation Satellite System (GNSS), of which the United States NAVSTAR Global Positioning System (GPS for short) is the most familiar component. In fact, "GPS" is often synonymous with satellite navigation, even it is now one of three global satellite navigation systems in operation along with the Russian GLONASS and EU Galileo satellite systems (they will be joined by the Chinese BeiDou-2 system when it expands to global scale in the early 2020s), While this article is specifically about NAVSTAR GPS, the basic operating principles are similar across the various GNSS implementations.
GPS was developed by the United States Department of Defense to provide a satellite-based navigation system for the U.S. military. It was later put under joint DoD and Department of Transportation control to provide for both military and civilian navigation uses, and has become a part of daily life. Most recent-model cars are equipped with built-in GPS navigation systems (increasingly as standard equipment), you can purchase hand-held GPS navigation units that will give you your position on the Earth (latitude, longitude, and altitude) to an accuracy of 5 to 10 meters that weigh only a few ounces and cost around $100, and GPS technology is increasingly found in smartphones (though not all smartphones derive location information from GPS satellites).
