What is GPS?
Its full, unglamorous name is Global Positioning System. Launched by the U.S. military in 1990, GPS is a network of 24 global positioning satellites that orbit the planet, beaming radio signals back to Earth to receivers in cars, boats, planes, and hikers' hands.
How Does It Work?
After acquiring radio signals from three or more satellites, a GPS receiver can triangulate your position and display it on-screen as a set of latitude/longitude or UTM coordinates. (Don't worry. We explain UTM on page 65.) Once it picks up four or more satellites, you get your position in three dimensions, including altitude. It's the world's most precise way to navigate; the typical accuracy of a hiker's unit ranges from 3 to 30 meters.
Will It Help You?
GPS will tell you exactly where you are at all times, regardless of visibility, as long as your unit is turned on and has acquired satellite signals. Or you can use it like a sighting compass, following an arrow on your screen.
The coolest tool in GPS is the waypoint, a digital sort of trail sign. A waypoint is a point on the Earth's surface-a trailhead, a waterfall, a pub, your home-whose coordinates your GPS will save at the touch of a button. Here's what waypoints can do for you:
Help you explore off trail: What's beyond that ridge? Wander right over, storing waypoints as you go to create a virtual trail for the way back. Or draw a cross-country route on your computer for a 30-mile loop in Denali, download it to your GPS, and follow the blinking arrow from waypoint to waypoint.
Remember points of interest : Want to save the location of that secret fishing hole, campsite, or food cache? Just hit the waypoint button; most units store at least 500 of them.
Follow routes: Download waypoint collections from a computer to share hikes with friends or explore a park you've never visited on a route you designed online.
Get found: With fresh batteries and some practice, you can't stay lost. Just click to your unit's Go To page and select the "trailhead" waypoint for the route back to your car. (You saved it, right? If not, you can create it by pinpointing the coordinates on a topo and keying them into your unit.)
Multitask: But wait, there's more. Many units come with altimeter, barometer, and clock. And all of them can crunch data on time and distance.
>>> Learn your average travel speed, estimated time to camp, vertical gain or loss, and exact trail mileage.
>>> Back home, plot your route on an aerial photograph, create an elevation profile, or plug your numbers into fitness-training software that analyzes each workout.