There’s a reason why many people have renditions of old-fashioned compasses tattooed on their shoulder or forearm: A compass is a powerful symbol of staying found; and body art metaphors aside, it’s still the best battery-free tool for getting around in the outdoors, especially compared to the finicky and sometimes less than accurate compass apps that can be downloaded to a smartphone. With a little practice, a map and compass duo is also very easy to use. Here’s a primer.
Orienteering compasses were invented in Scandinavia nearly a century ago. This style of compass has several key features: a clear baseplate with straight edges (A); a rotating dial (B), with direction (North, South, East, West) and corresponding degree (0-360) indicators; a magnetized needle floating within the dial (C); a red orienting arrow etched in the base of the dial (D); orienting grid lines (usually red or black) within the dial (E); and a marker on the baseplate at the top of the dial, known as an index mark (F), where directions are read.
Some orienteering compasses also have sighting mirrors, which improve accuracy. The best compasses are made by manufacturers like Suunto, Silva and Brunton.
Orienteering compasses work like a protractor to calculate directions from topographic maps and marine charts. To navigate in a straight line from one point to another, you must first identify your starting and ending points on a map.
Use the baseplate of the compass to create a straight line between your starting point and your destination, with the index mark facing your direction of travel. Next, rotate the dial of the compass so that north on the dial is aligned with the top (north) on the map. Match up the orienting grid lines within the dial of the compass with the grid lines on the map to fine-tune your alignment. Once you’re satisfied the compass and map are in alignment, read the direction (aka “Bearing”) from the index mark. For this process you can ignore the magnetized needle when calculating a direction. In the case of measuring a direction across Havilland Bay, our bearing is 296 degrees.
A direction measured from a map is known as a true bearing; that is, the direction is measured in reference to true (or, more accurately, map grid) north. However, a magnetized needle in a compass is attracted to magnetic, not true, north. This difference is called “magnetic declination.” Declination varies across Canada, with values in Ontario spanning about 10 degrees. The value for your location can be determined with an online calculator or from the legend on the right-hand margin of Canadian topographic maps. (You can use the links below to help with this.)
In my hometown of Sault Ste. Marie, for example, declination is approximately 8 degrees west of true north. Therefore, to compensate for this difference a navigator must add 8 degrees to any direction measured from a map before using the compass in the field. A mnemonic is the easiest way to remember how to deal with declination: Declination west is best, or added to the true bearing; declination east equals least, or subtracted from the true bearing. So in the case of our example, our magnetic bearing—or the direction we’ll follow on our compass to boat across Havilland Bay—will be 296 + 8 = 304 degrees. Some orienteering compasses have an adjustable dial to allow you to compensate for declination without doing any math; if you have this type of compass it’s important to check the setting and make sure it is correct for your location to avoid error.
Hold the compass level and at waist height, away from anything metallic (such as belt buckles or phones), so you can see the dial.
You can also hold the compass at eye-level and angle the mirror to view the dial.
Rotate your body (or boat) so that the floating magnetized needle becomes aligned with the red orienting arrow in the compass dial. At this point you are facing your destination. Sight a target along your bearing to follow a straight line; in a forest, this may be a prominent tree or rock outcrop. Walk to your target and repeat, pivoting to align the needle in the orienting arrow and sighting another target along your bearing. When travelling on the water, set your compass in a location that’s level and away from anything metal, and steer to keep the needle aligned with the orienting arrow, with the index mark aligned with the bow of your watercraft.
The value for your location can be determined with an online calculator or from the legend on the right-hand margin of Canadian topographic maps.
Orienting the Map to North
Besides enabling you to travel in a straight line through a dense forest or across a foggy bay, a compass can also be used to make sense of your surroundings. This is called orienting your map to the north.
Start by rotating the dial of the compass so 0 degrees (or N) is aligned with the index mark at the top of the dial. Set the compass flat on your map, align the orienting grid lines in the compass dial with the grid lines on the map (so that the map is north-side up), and rotate the map and compass together so that the magnetized needle is aligned with the orienting arrow. At this point the map is oriented with your surroundings, allowing you to visually identify prominent landmarks in your surroundings.
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