GPS Units - Appalachian Mountain Club

GPS Units

April 22, 2005

AMC Outdoors, May 2005

We skied uphill through fog and falling snow, zig-zagging around crevasses bigger than Olympic swimming pools. We were on a six-day March traverse of the Wapta Icefield, a sprawling starfish of glaciers in the Canadian Rockies. At a pass called Balfour High Col, a frigid wind blew snow sideways in a whiteout so absolute that twice I toppled onto my backside from vertigo, uncertain whether I was moving or standing still.

Several miles of glacier separated us from the next hut; and somewhere in this gumbo atmosphere lurked sheer cliffs that had claimed the life of a skier in similar whiteout conditions the year before. With two of us holding GPS receivers pre-programmed with our route, guided by the screen’s little arrow while watching for crevasses, the five of us safely reached the hut—and collapsed gratefully inside.

Without GPS, we could have slowly navigated by map and compass, but I doubt that we would have reached the hut in daylight, and spent the night, cold and wet, in a snow cave instead.

For most Northeast hiking, we seldom need more than a map, and occasionally a compass, to find our way. But for navigating severe weather and whiteout conditions above treeline, or finding your way home through thick off-trail forest or a dense ocean fogbank, a GPS receiver can be a very handy—and potentially life-saving—item.

Putting your tax dollars to work

The U.S. Defense Department spent $12 billion to create a Global Positioning System of 24 satellites that circle 12,000 miles abovet the Earth. By locking onto the signals from any four of these satellites, a GPS receiver can calculate your position anywhere on the planet, generally within 50 feet and often within 20 feet, making it the most precise navigation system ever devised. In the U.S., “WAAS-enabled” units—which receive GPS signal corrections from a system of satellites and ground stations—are accurate to 10 feet or less 95 percent of the time.

After pinpointing your location, a GPS unit displays your coordinates in either latitude and longitude or UTM (Universal Transverse Mercator; see sidebar). In order to identify your position, however, you will still need to know how to plot those coordinates on a map.

A GPS unit not only identifies your exact spot on the planet, but it can also store that location’s coordinates—called a waypoint—for later reference. Once a waypoint is saved, the GPS unit can point you toward it at any time from your current location, providing a precise compass bearing to follow and the distance you need to travel in order to reach it. For example, by recording a waypoint for the trailhead parking lot, or your sea kayaking put-in spot, you’ll be able to easily navigate back to it if you become disoriented or lost.

GPS units can store hundreds of waypoints, which you can arrange in customized routes (sequences of two or more waypoints). You can load known waypoints onto a GPS receiver prior to a trip—either by manually entering them or downloading them directly from a computer—and use the unit to stay on route, as we did on the Wapta Icefield. A GPS unit can also record your route, or “track,” as you hike, allowing you to retrace your steps.

Most GPS receivers can be plugged into your personal computer and, with necessary software, can upload or download waypoint and map data. While many receivers come with a base map of roads, rivers, and public-land boundaries, they do not show trails or topography. Used in conjunction with mapping software, however, pricier models can store and display actual topo maps. The relatively small screens allow you to view only a small area, however, and the resolution currently does not approach the quality of a good paper map.

GPS isn’t without weaknesses. Dense vegetation and landforms can block satellite signals and affect the receiver’s ability to fix your position. GPS units rely on batteries, which typically only last for 10–20 hours of continuous use. And GPS units are not compasses, and will not indicate direction (though some models come with a built-in electronic compass).

For all of these reasons, a GPS unit should not be considered a stand-alone navigation tool. Always carry a paper map and handheld compass with you as well—and know how to use them.

Maps, memory, and money

Most recreational GPS units weigh half a pound or less, fit readily in a pocket, and range in price from roughly $100–$500. Every GPS unit on the market, including the most basic, allows you to pinpoint your location, record waypoints, and navigate to them. The primary differences between models—and what drives up the price—revolve around memory and the display screen.

The graphic information contained in maps requires considerably more memory than is needed to record simple numeric coordinates. Many models under $200 provide only one megabyte (MB) of memory, which is adequate for storing waypoints and routes, but is insufficient to store or display maps. For mapping capabilities, a minimum of 8MB is necessary. The more memory the unit has, the more maps—and greater coverage area—it can store. Models with 8MB start around $200, while several $500 units now offer more than 100MB.

Color displays and higher screen resolution also bump up the price. While these features are useful for viewing maps, they provide little benefit when recording and navigating to waypoints.

Other features to look for when shopping for a GPS unit are increased WAAS-enabled accuracy, which is not available in some of the most basic designs; and a button layout that is easy to manipulate, even when wearing gloves. And remember that all the memory in the world won’t help if your GPS dies and you forgot to bring spare batteries.

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Michael Lanza

AMC Outdoors, the magazine of the Appalachian Mountain Club, inspires readers to get outside and get engaged. Learn more.