Global Positioning System (GPS) devices are a relatively new navigation invention, considering we've been using compasses and maps for hundreds of years. Used by the military for years, the government opened up GPS satellites for civilian use in the 1980s.
A network of 24 satellites orbits the Earth twice a day, transmitting signals back to earth. A GPS receiver locks onto signals from three or more satellites to determine your location, using a method called trilateration. Your receiver calculates the difference between the time a satellite sent a signal and the time your system received it. Using the information gathered from several signals, the receiver triangulates your exact position. It can even determine how fast you're going and how long it will take you to reach your destination. GPS receivers are extremely accurate, many within 50 feet (15 meters) [source: Garmin].
Many GPS devices come loaded with maps that work in conjunction with the information from the satellite signal. Depending on the particular GPS unit you purchase, your device could come with road maps, marine maps, topographic maps, trail maps or ski resort maps. Keep in mind there are different GPS units for road travel, cycling, running and fitness, boating, fishing, flying and hiking. If your unit isn't loaded with the maps you want, you can purchase and download specific maps to the device. Maps vary widely in price. You can find some maps (like maps of national parks) online for free, or you can purchase device-specific maps from the manufacturer for around $100.
You're probably familiar with using a GPS system in your car. Simply enter an address and the device will calculate a route there and a route home. Some systems will even take into account traffic and construction conditions. But how does a GPS steer you in the wilderness?