Getting on Course

Photo Essay: Hiking the Andes with Mountain Lodges of Peru

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Every year, members of the famed Appalachian Mountain Club rescue scores of lost hikers and campers, most of whom have a compass in their pocket when they're found.

If asked, "Why didn't you use your compass to find your way back to camp?,"  they invariably reply: "I tried. . . but I didn't know how. "

When AMC rescuers question why these people insist on carrying an instrument they don't know how to use, an overwhelming majority respond by stating that "everyone should carry a compass in case they get lost!"

So much for logic.

Fortunately, anyone can learn the basics of backcountry navigation in a few hours, if he or she is willing to make the effort.

The Map

Except for going in a straight line, a compass is useless without a map. Any map—even a photocopied State Park trail guide—is better than no map at all. A map provides the directions you need: The compass is merely the tool that enables you to follow them!

Get the best topographic maps available. These can be purchased from two major sources:

To order United States maps, write to:
U.S. Geological Survey
Map Distribution Section
Federal Center
Denver, Colorado 80225

To order Canadian maps, write to:
Canada Map Office
615 Booth St.
Ottawa, Ontario, Canada K1A OE9

For advance trip planning, it's best to write the appropriate map office and request a free index to topographic maps. These indexes tell what maps are in print, in what scale, and the cost. Rather than bore you with the complexities of the many scales available, suffice it to say that the larger the scale, the more useful the map.

In American maps, your best bet is to get 1:24,000 (one inch on the map equals 24,000 inches-or 2,000 feet-on the ground) maps. When traveling in Canada, the 1:50,000 (1 1/4 inches to the mile) quadrangles are ideal.

When maps arrive, outline your route and tick off the proposed mileage. This way, you won't attempt to cover more distance than you're capable of.

Finally, waterproof your maps with a chemical preparation. I've had good luck with "Storm proof," (write the Martensen Co., P.O. Box 261, Williamsburg, VA 23185), and "Thompson's Water Seal"—an industrial strength compound that's used for sealing concrete block. You'll find Thompson's Water Seal on the shelves of most hardware stores in aerosol cans and tins. I buy it by the quart and apply it to maps and journals with a polyurethane foam varnish brush. The product also does a fine job of waterproofing hats and clothing. Water-resistant maps should be further protected by sealing them inside a plastic map case.

Interpreting Contour Lines

You can't appreciate the value of a good map until you understand how to interpret contour lines. These basics will get you through:

1. Contour lines are light brown lines on a map which connect points of equal elevation. Thus, closely spaced lines indicate lots of elevation change, whereas wide-spaced lines show the opposite.
   
2. The closed or "Vee" end of a contour line always points upstream.
   
3. Where contour lines cross or run very close together, you'll find an abrupt drop-a falls or canyon.
   
4. The vertical distance between contour lines is called the contour interval, and its value is given in the map legend. It is not the same for all maps.
   
5. The larger the contour interval, the more difficult it is to determine the characteristics of the land. In short, a map whose CI = 10 feet, gives a much clearer picture of the topography than one whose CI = 100 feet. Note that foreign maps give all information in meters, and these will need to be converted to feet to be meaningful to most Americans.

There are a number of different compass types, but only the versatile Orienteering model, pioneered by Silva, makes much sense for traveling the backcountry.

Orienteering models have built-in protractors which allow you to quickly and accurately compute direction and scale distance without first orienting the map to north. This means you can define a precise direction to the nearest degree while hustling down a wilderness trail! Additionally, your direction of travel is physically set on the compass by turning a dial. There's nothing to remember and nothing to write down.

Basics First

First, learn the compass rose and memorize the bearings (degree readings) of the eight principal points. Before you determine the direction of travel from a map with the protractor function of your compass, ask yourself: "What's the approximate bearing to my objective?" Use common sense —make sure your estimate roughly agrees with the bearing you computed from your map. This procedure will eliminate the two most common compass errors—the 180-degree error (you go north instead of south) and the 100-degree error (you travel at 240 degrees instead of 140 or 340). It's amazing how flustered you get when you're uncertain of where you are. In fact, lost persons have been known to read their compasses backwards.

If you know the approximate direction of travel before you read your compass, you'll eliminate all errors which result when transferring information from the map to the ground.

Declination

A compass needle points to magnetic north, not to true north, and this angular difference, called declination, must be considered whenever you use your compass (see Figures 9-5 and 9-6). In the eastern United States, the declination is westerly; in the western United States, it is easterly. If you live right on the imaginary line which goes through both true and magnetic north poles (called the agonic line) your declination will be zero.

In the northeast, the compass needle points more than 20 degrees west of true north, while in the far west, it errs by as much as 21 degrees east. Since one degree of compass error equals 92 feet per mile of ground error, you must take this difference account when you navigate.

Maps are always drawn in their true perspective, so any bearing you compute from them with the protractor function of your compass (no magnetic needle) will be a true geographic direction. This true—or map—bearing must be changed to a magnetic bearing to be set on your compass. There are two ways to make the conversion:

First, buy a compass which has a mechanical device for offsetting the difference. Second, apply the rhyme, "Declination east, compass least (subtract east declination from your map direction)." Or, "Declination west, compass best (add west declination to your map direction)."