Many years ago, I picked up a pamphlet from Silva, the compass maker, with the words “Read this, or get lost” on it. Inside is advertised the company’s “easy as 1-2-3” system for finding your way in the woods. Impressed by the simplicity of the concept, I replaced my clunky old lensatic compass immediately with a Silva Polaris Type 7 compass and have never looked back.
The ability to read a map and use a compass are essential skills every hiker should have in their toolkit. With some rudimentary knowledge and a little practice with both you can really up the ante on your confidence level and safety factor in the outdoors and better enjoy your time on the trail.
Let’s start with the parts of a compass. First, there’s the flat “baseplate,” and near the top center of that, the “direction of travel arrow” at the end of the “index line.” Below this is the round compass housing with a “360-degree dial” and “north sign,” within which is the floating “magnetic needle,” the “orienting arrow” beneath it, and “orienting lines” to either side.
The magnetized red end of the compass needle always points north, not to true north, but rather to magnetic north. True north is the geographic North Pole, where the imaginary 360 lines of longitude meet at the top of the planet, while magnetic north is found at the tip of the Earth’s massive magnetic field located in the Arctic Ocean. The difference in degrees between true north and magnetic north is known as “declination.”
USGS topographic maps, National Geographic/Trails Illustrated maps, AMC trail maps and the like are all oriented with true north at the top of the map. Each also shows a declination diagram in its legend. In Maine, magnetic declination currently varies between 14-1/2 and 17 degrees west of true north, depending on your location.
Spread your map out on a table and let’s do a quick exercise. Choose an obvious place on the map, the intersection of two roads, perhaps, and mark this as your starting point. Pick another known spot, like a mountaintop, and mark it as your destination. Using the edge of the compass baseplate, draw a line connecting the two points. Holding the compass there, turn the compass dial so that the orienting arrow aligns to true north (the top of the map). The angular difference between true north and your drawn line measured clockwise is the “map bearing.” Call it 45 degrees for this example, read from the index line on your compass.
Since your compass points to magnetic north, to actually travel in the field between those two points, you’ll need to adjust the map bearing to a “magnetic bearing” by compensating for declination. Use 16 degrees west for the purpose of this exercise. Way back when, I learned the mnemonic “west is best, east is least,” and have used this trick ever since to remember to add whatever the west declination is (west is best = add) to the map bearing to convert to a magnetic bearing.
In this case, to add 16 degrees, turn the compass dial to the left until the 16-degree mark is at the top. Notice that doing so causes the red end of the magnetic needle to align with the orienting arrow, a procedure called “boxing the needle.” You should now read 61 degrees at the index line (45 degrees + 16 degrees); this is your magnetic bearing and the direction you’ll travel on the ground along your plotted line.
If you were physically at the starting point right now, you’d hold the compass level in your hand, orient yourself with the compass by rotating your body until the red end of the needle is over the orienting arrow, sight on a landmark ahead of you (if possible) with the direction of travel arrow and start walking. To return to the starting point from your destination, simply backtrack by boxing the needle in the reverse.
It pays to refer to your compass and map often to stay on track and properly oriented with the terrain features around you. You might even try your hand at plotting your position en route. To do this, you’ll need to identify by sight two known objects and mark them on your map. Then take a bearing to each object. Convert these magnetic bearings to map bearings by subtracting the west declination from each reading. Plot these lines on the map and where they intersect is your location.
Proficiency with map and compass takes some practice. Buy a good reference book and consider taking an orienteering course to get a leg up.
Carey Kish of Mt. Desert Island is the author of AMC’s Best Day Hikes Along the Maine Coast and editor of the AMC Maine Mountain Guide. Follow Carey’s adventures on Facebook @CareyKish