We may earn revenue from the products available on this page and participate in affiliate programs. Learn more ›

Perhaps you’re occasionally checking your smartphone’s built-in mapping software while driving to a remote trout stream, or using Google Earth on a home computer to scout out new hunting and fishing destinations. Maybe you regularly rely on a dedicated GPS device like a handheld navigator or dog collar to keep track of whereabouts afield. Regardless of how you enjoy the outdoors, like most hunters and anglers these days, you’ve probably tapped into the Global Positioning System in one way or another to improve your outdoor experience. But how does GPS work?

Since the U.S. satellite-based system initially limited to military applications was fully opened to civilian use in 2000, sportsmen have been among the most ardent adopters of GPS. But how much do we really know about the technology behind this space-age wonder?

If you’ve ever found yourself turned around in the backcountry, or just wanted to gain some perspective on a piece of ground you’re hunting for the first time, you’ve likely heeded a basic principle of wayfinding: Head for high ground. By hiking to the top of a rise or simply climbing a tree, you can improve your vantage point and gain a better perspective on your surroundings. The Global Positioning System uses the ultimate high ground—space—by deploying a system of multiple satellites positioned around the globe. Each satellite is constantly sending a unique radio signal relaying its location, speed, and time of broadcast to ground stations and to GPS receivers built into watches, mobile phones, and dedicated GPS devices. 

By combining data from four satellites at once, a GPS receiver can pinpoint its position on the globe through a process called trilateration. Here’s how it works.

When the forerunner of today’s Global Positioning System was launched by the U.S. Navy in 1957 to track submarines during the Cold War, GPS was largely a military technology inaccessible to consumers. That began to change in 1983, when the U.S. announced it would make GPS available for civilian use as a way of improving aviation safety, which led to the introduction in 1988 of the first hand-held GPS device (Magellan’s NAV 1000, a 1.5-pound, $3,000 device with just a couple of hours of battery life). But in 1990, the U.S. Department of Defense began decreasing the accuracy of GPS readings for nonmilitary users. Selective Availability, as this degradation of GPS accuracy was known, was discontinued in 2000, giving consumer users the same precision long enjoyed by the military. GPS devices now are accurate to within 7 meters (about 22 feet) anywhere on the planet around 95 percent of the time.

What about the other five percent of the time? There are several factors that can affect GPS accuracy.

The constellation of 31 GPS satellites developed and operated by the U.S. is just one of four global positioning systems that are currently operating in medium earth orbit. The other three are Galileo, developed and operated by the European Union; GLONASS, developed and operated by Russia; and BeiDou, developed and operated by China. Japan and India also have plans to expand their regional satellite tracking systems to global coverage.

GPS satellites circle the earth twice a day at an altitude of 13,000 miles while traveling at a speed of 8,700 miles per hour. Between them, the four global satellite tracking systems have around 115 satellites in orbit.

In addition to pinpointing location, GPS data is useful for tracking, navigation, setting waypoints and as the basis for a wide range of research projects on animal behavior, from the usage of core areas by whitetail deer to the transglobal migration of large ocean predators such as great white sharks and bluefin tuna.