Dorothy Gale had it easy—she needed only to follow the yellow brick road to find her way to the Emerald City. Now, thanks to the increasing affordability of Global Positioning System (GPS) devices, we have it just as easy if not easier. With features like turn-by-turn directions and voice prompts, finding your way to and from your destination is akin to clicking your heels three times. Developed by the US Department of Defense for military tactics, GPS technology is a 24/7 radio navigation system that identifies and tracks the location of the GPS device virtually anytime, anywhere.   GPS devices get their data from 24 satellites orbiting Earth. Locking into a minimum of three satellites determines your location in longitude and latitude. Some devices routinely lock into four satellites to provide altitude. Use of the satellite network is free—all you need is an unobstructed view of the sky, but while GPS devices will work under cloud cover and inside cars, they may falter under heavy tree canopies, inside tall buildings or tunnels, or dense urban areas with lots of skyscrapers. Pronto’s Auto GPS Buying Guide will help you select the GPS device that meets your needs (see also Handheld GPS Buying Guide).  More »