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Real-World Global Positioning and Electronic Maps

A guidebook author explains where he's coming from and how he gets there using innovative electronic navigational tools

By Bruce Grubbs

RESOURCES

BOOKS
Grubbs, Bruce; Basic Essentials Using GPS;
The Globe Pequot Press; 2005

Grubbs, Bruce; Best Loop Hikes Arizona;
Mountaineers Books; 2004

Steck, George; Grand Canyon Loop Hikes;
The Globe Pequot Press; 2002

COMPUTER MAPS
Delorme, (800) 561-5105, www.delorme.com

National Geographic Maps, (800) 962-1643,
maps.nationalgeographic.com/topo

Maptech, (888) 839-5551, www.maptech.com

A friend thinks the most useless item to carry on a hike is a GPS receiver. The second most useless item is a compass. He's nearly right. Much of the time, a good map is all that is needed to navigate in the backcountry. Here in the Southwest, where hundred-mile visibility is normal and the rugged topography provides plenty of landmarks, the classic map and compass techniques don't really apply. You'll learn why at your first attempt at walking a compass bearing in a place such as the Maze, the San Juan Mountains, or the Grand Canyon - in time you will encounter a slot canyon or cliff that will require a major detour.
That's where maps come in. Traveling cross country, a good map is essential. With a good map you can plan a route around obstacles and take advantage of easy terrain. With a map you can also find springs, rock tanks, and other water sources in the desert, and even locate outstanding campsites.
Topographic maps are the only useful maps for backcountry travel. Topo maps represent the terrain with contour lines and some will use shading to show relief. Among the best topo maps are those published by the U.S. Geologic Survey. Its 7.5-minute series of maps, published at a scale of 1:24000 (or 2,000 feet to the inch), cover the entire country. The maps represent the terrain and other natural features with extreme accuracy. They also show man-made features that were present when the map was published. But it takes thousands of maps to cover a western state - it's impossible for USGS to keep all those maps up to date.

THE COMPASS

After all the bad things I said about compasses, I still carry one on every trek except easy, short trail trips. And often I carry a GPS. Part of the reason is that I often need to map a trail or a route for possible inclusion in a book, since I'm a guidebook author. I owe it to my readers to describe and map a trail as accurately as possible, and I can map a trail much more quickly and accurately with GPS and a topo map than I can with only a map or map and compass. But even when I'm not doing professional field work, I'm surprised at how often I've found a GPS useful, or even essential; with the same said for a compass.
A classic desert navigation problem often arises when attempting to locate a road access into an interesting area. Because the desert is so open, people often make new roads somewhat casually, which can lead to confusion. On the ground, you'll often encounter road junctions where the latest topo or road maps show nothing. Too commonly there is no sign to indicate where to go. In this situation, I turn to map and compass work to find my position and to help me decide which road to take.
To use this method, called "triangulation," you find three or more landmarks that are distinctive both on the map and in the terrain. Then, with a compass you sight on the landmarks and take bearings from each one. Finally, you plot all the bearings on your map. The point where the bearings cross is your approximate location. Triangulation works, but is time-consuming. I've encountered numerous such road junctions on exploratory trips and burned up hours driving stray roads trying to find an interesting canyon or other destination. I'd rather spend that time hiking or biking, not driving. And often there just aren't enough good landmarks to triangulate, even in the open desert. In forest it's usually impossible.
Here's where GPS comes in handy. In just a few seconds you can get an extremely accurate position with the GPS receiver. Plotting accurately your position on the map can take a little more time, but this method is still far faster and more accurate than triangulating with a compass. And it works nearly everywhere, even in dense forest and in bad weather with no visibility.

GOTCHA

There are a few "gotchas" with GPS, of course. A decent view of the sky is required in order for the receiver to pick up enough satellites (four or more) for an accurate "fix." You won't be able to get a position in a deep, narrow canyon, for example.
A more serious problem is using the wrong settings in your GPS. Maps are referenced to standard reference points, called "datums." As mapping standards evolved, many different datums have been produced in different countries and regions. For example, most USGS topo maps use NAD27 (North American Datum of 1927). But GPS uses WGS84, the World Geodetic Survey of 1984. By default, your GPS receiver is set to WGS84, so if you plot your position on a map that uses a different datum, you can be off by as much as several miles. The solution, obviously, is to set the GPS to use the correct datum. The receiver still uses WGS84 internally, but translates the coordinates to the map's datum for display.
Another GPS "gotcha" is plotting coordinates on a map. By themselves, the numbers on the receiver's display are useless data. You have to plot the location on your map as a "waypoint" for it to mean anything. Nearly every map used for navigation have one or more coordinate systems printed on it. Universal Transverse Mercator (UTM) is the easiest system to use. UTM is a system of square grids, marked on the margins of the map every 1,000 meters or so, depending on the scale of the map.
Because it's a linear, square system, it's fairly easy to plot locations on the map. For a while, USGS was publishing its 7.5-minute series of topos with a 1,000-meter UTM grid printed on the map, which was really helpful. You can always grid a map yourself, but this becomes tedious if you have many maps.
The latitude and longitude system is even harder to use. While lat/long is universal and is always found on good maps, it's difficult to use in the field without a lat/long plotter scaled for your map. The reason is that the lat/long system is not linear - it changes with changes in latitude.
In the lat/lat long system, coordinates are expressed in degrees of longitude east and west of the Prime Meridian, a north-south line that runs though Greenwich, England. Latitude is the number of degrees north or south of the equator, which is zero degrees latitude. Degrees are further divided into minutes, which are 1/60 of a degree.
When the lat/long system was designed, ocean sailing was the major navigation problem, so the system was designed so that one minute of latitude was one nautical mile, which is really handy on the sea but not so useful on land. Even worse, lines of longitude (called meridians) converge as you head north or south toward the poles, so one degree of longitude is only one nautical mile at the equator. Anywhere else, it's less.
You can see this effect for yourself on any 7.5-minute topo map of the Four Corners region. The 7.5-minute maps are called that because they cover a quadrangle of latitude and longitude 7.5 minutes on a side. Just measure the top of the map and the bottom and you'll see the difference. That's why it's so hard to plot lat/long waypoints on a topo map without a special plotter.
The final "gotcha" is the difficulty of taking plotted locations from a paper map and entering them into your GPS receiver. This occurs with advance planning at home, when you want to enter key locations in the receiver for field use. But entering coordinates on the limited keypad of a typical GPS receiver is a human-error-prone process.
Here's where computer-based, electronic maps come into their own. Because the new worldwide standard datum for mapping is WGS84, all the computer-based maps use WGS84, eliminating that potential source of error. Plotting coordinates on a computer map is just a matter of pointing and clicking. And getting them into your receiver is a simple as connecting a cable and issuing a menu command to transfer the data from the computer. Data transfer works just as well in reverse - save locations in the field on your GPS unit and then transfer them to your computer maps at home.
Computer maps have many other advantages over paper maps. For one, they are cheaper than paper maps. You can buy a set of CD-rom's or a DVD covering an entire western state for $100. In paper form, the same coverage would cost around $10,000.
Most of the commercial topo map sets, while based on USGS topo map data, include more up-to-date data on roads and other man-made features. Commercial maps come with software that allows you to mark and name GPS coordinates as well as to create routes that can be uploaded to the GPS receiver. Computer map programs also have extensive trip-planning tools that let you design free-form routes, plot elevation profiles, mark locations with a variety of symbols, put text labels on the map, and make extensive notes and even link to photos keyed to specific locations on the map.
Most map software allows you to view terrain in three dimensions, which can be helpful for visualizing an unfamiliar area. And finally, you can print custom maps with your GPS waypoints, routes, symbols, and text labels - overlaid with a UTM grid in case you still need to plot a waypoint in the field.
It gets even better. If you have a laptop computer, you can hook up the GPS and create a moving map system, with your position shown continuously on a detailed topo map at any scale you choose. Even basic GPS units that don't have built-in maps can be used this way, as long as the receiver has a port for connection to a computer. And the moving map display on your laptop is far better than the tiny map display on even the most expensive hand-held GPS units. In fact, the two GPS receivers I currently use for field mapping have no built-in mapping at all.
Although I'm not going to use a laptop moving map system on a hike, I have found it useful when driving in remote areas while trying to find my way around a confusing maze of unsigned back roads. I plan in advance on my home computer and download the GPS data to the receiver - and print paper maps.
Here's an example of a Grand Canyon hike where GPS could have saved time and alleviated uncertainty for our group. The Grand Canyon is one of those places where GPS is usually unhelpful. The hiking is strenuous cross-country, and a route is entirely controlled by the terrain. Specifically, travel is usually along terraces bound above and below by massive cliffs. Often a change in level is required because the terrace you're hiking peters out or becomes too rough and slow, or you need to get through a cliff band to the Colorado River or a spring or water pocket. Routefinding is almost entirely by map and eyeball. Still, there are times . . .
This particular trip was a circumnavigation of Powell Plateau along the river, an excellent nine-day trip described by George Steck in his fine book, Grand Canyon Loop Hikes. We added to the loop and started from a different trailhead, but for this example I'll begin from the normal trailhead, Swamp Point - a place I've used as a trailhead for several trips. In describing the mechanics of navigating this route, I refer to National Geographic's Topo! Maps but other software can be used just as well.
Swamp Point is at the end of a maze of national forest and national park dirt roads that wander across the heavily forested Kaibab Plateau. Some of the road junctions are marked but the critical ones are not. On this most recent trip to Swamp Point, our group spent a lot of time hunting for the right roads. However, the next time I drive to Swamp Point, I'll do it using GPS. Here's how: On the Swamp Point map, I've marked each road junction with a waypoint. Naming a waypoint is limited by space in most GPS receivers, so I've named the waypoints JCT01, JCT02, etc. Because most receivers can store a comment with a waypoint, I added a comment to each waypoint showing which way to turn. JCT01 has a comment, "RIGHT WEST." This comment shows up on the GPS receiver's screen so I know which way to go: turn right, heading west.
Another convenient feature of the Topo! Software is the ease with which GPS routes can be created. By putting all the waypoints along the Swamp Point approach in a route and downloading it to the GPS unit, I can activate the route during the approach drive, and the receiver will show the distance and direction to each waypoint in turn.
With this route preloaded in the GPS, finding the trailhead will be a snap. I've used this method many times on other approach drives.
On the first part of the loop hike, permanent streams and water is luxuriously plentiful. Soon after the walk continues along a terrace known as the "Tonto Plateau." This steeply sloping terrace begins just above the Colorado River, and access to water is easy. But as the days of hiking pass on the Tonto, the strata rises and the river becomes difficult to reach. Water can be found often in side canyons, but these sources eventually become scarce. When author Steck first worked out the loop, he discovered he was facing an apparently waterless section at the southernmost part of the loop. This section is especially frustrating because the river is often just a few hundred feet below, but blocked by the Tapeats sandstone, which forms a continuous, 200-foot cliff.
In the course of his explorations, Steck found a spring which appeared to be reliable. The location and existence of this spring was key to safely accomplishing the route, so he promptly named it "Key Spring." On a subsequent hike on the south side of the river, Steck spotted a ravine that appeared to offer a route through the Tapeats cliff on the north side of the river, at the southernmost point of the Powell Plateau loop. When I did the loop with two friends, we found Key Spring and the ravine to the river, but also two new routes to the river, one to the west and the other to the east. With these four water sources, what started as a dangerous section of the hike is now much safer.
Since none of these places are marked or named on the USGS topo map, I would carry my smallest GPS receiver, a Garmin Fortrex 101, on any repeat of this hike - especially in hot weather. Using Topo! before the trip, I would mark a waypoint for each of the water sources and download them to the receiver. Not only would I be assured of finding these critical points, but I would have the GPS along to mark any other important points on the route.
While no substitute for traditional map and compass skills, the combination of computer-based maps and GPS is extremely helpful both for planning backcountry trips and for saving time in the field. The end result is that I get more time to enjoy the wilderness.

Bruce Grubbs he is an active outdoor writer and and photographer with 20 books in print. His "day job" is flying air charters. His web site is brucegrubbs.com.