Compass Manual

The Compass Manual By: Joe Gilmet

The important part of a compass is its magnetized needle, balanced on a pinpoint and free to swing around. When left to itself, the needle always points to the magnetic North, which is the northerly direction of the earth’s magnetic force lines. This end of the needle is usually marked with the initial “N”, shaped like an arrowhead, or colored so you can tell which end of the needle is pointing north. There are several types of pocket compasses. The best of these has a liquid-filled dial which slows the swinging of the compass needle and makes it easier to use. The compass dial is divided into 360 parts. These divisions are called degrees and each degree represents a bearing or direction. The degrees are measured clockwise from North, which is called 0° or 360° on an Orienteering Compass. This is the compass most commonly used. The four cardinal directions,North, East, South, and West, are at right angles to each other (i.e. N-0° or 360°, E-90°, S-180°, and W-270° ). Using a Compass Compasses can be used three ways without a map. 1. To find directions or a bearing from one point toanother. 2. To follow a bearing from one point to another. 3. To return to a point of departure after traveling on a bearing. The modern orienteering compass gives directions and bearings quickly. To find a bearing with this type of compass: (A) Hold it level in your palm at about waist height in front of you, then turn and point the directional arrow where you want to go. If the compass is not held level, the needle may show an inaccurate reading. (B) Orient the compass by turning the compass housing until the North end of the orienting arrow is under the North end of the compass needle. (C) Read the bearing in degrees where the tail of the directional arrow meets the degree scale on the housing.

Some compasses have other indicators to show where you read the bearing. To follow this or any other bearing is also a simple matter. With the needle and orienting arrow properly aligned, pick out a landmark along the line of sight and walk to it. When you reach the landmark, orient yourself again, walk to your next landmark and so on. It is a good idea to write the bearing down, if possible, because a twig or limb may touch your compass housing and move it.

To return to your starting point, turn around, orient your compass to the opposite bearing, and using landmarks as before, walk to it. This is called “using the reversed bearing”. Thus, if you were traveling on a bearing of 60°, the reverse bearing would be 60° plus 180° = 240°. A landmark should be chosen that is on the course of the hunter’s ultimate destination and one which will be visible until it is reached. On reaching the marker, the hunter chooses another landmark in the distance and checks the bearing again with the map and compass. In a forest, a straight course can be maintained by lining up two trees and walking directly toward them. As the first tree is reached a third tree is lined up, behind and in a straight line with the second. This procedure is repeated each time another of the trees is reached. A common mistake when using a compass is to look at the bearing too often. Renew your bearing only as often as the distance between good landmarks dictates. This distance will vary with the terrain, cover and visibility, ranging from 3 to 20 meters in thick brush orfog to 0.5 km or more in open country on a clear day. Remember too, that a compass can only give you the direction you want to travel, but cannot tell you where you are. You should have a general idea where you are before you try to use a compass. Therefore, before entering the woods, always take time to check the bearing of the highway you are leaving and the direction you are traveling. Then, if you get “turned around”, the reverse bearing will take you back. Because a compass is equipped with a magnetic needle, be careful to keep it away from all iron-bearing metal and electric currents. This includes axes, knives, guns, fishing rods, bridges, railway and fence lines, cars, rings on fingers, watches, etc. Sometimes even the zipper on a jacket may cause the needle to change direction. Power lines will do the same. When camp has been set up beside a “baseline” such as a river, road or railway, you can easily find the way back to camp with a compass. If you are hunting north of the base-line, you know that as long as you don’t cross that base-line, all you need to do to find camp is walk south from where you are and you will be in line with camp. Referring to a map, you should know if you are above or below the camp. A compass is best used in combination with a map. The map will show which direction to take to get to a specific location. The compass will keep you walking in the right direction.

Maps A map is best defined as a reduced diagram of a portion of the earth’s surface as viewed from directly above. Have a map of the area in which you plan to hunt and study it in advance. Road maps are not always drawn to scale and often lack sufficient detail to be of use for anything but a highway and road guide. The preferred map for most uses is the Topographic Series at a scale of 1:50,000. These are detailed maps showing the elevations of hills, valleys and landmarks such as roads, lakes, vegetation, swamps, and buildings. Key elements of topographical maps include:

Legend: a listing of symbols shown on the map and what they mean. Scale: provided as a ratio. For example, on a 1:50,000 scale map, one unit on the map equals 50,000 of the same units on the ground. Contour lines: a contour line shows the outline of a hill at one elevation. Widely spaced lines indicate a gentle slope. Closely spaced lines indicate a steep slope. True and magnetic north arrows: indicate the direction of true north and magnetic north. Most maps are oriented so that true north is at the top of the map sheet. A compass, however, points to magnetic north. Grids: a series of vertical and horizontal lines that mark the map off in a grid system. Topographic maps show both geographic (latitude/longitude) and UTM grids (kilometers) that make it possible to determine your precise location. In the Atlantic Provinces topographical maps are available from various private and government sources. Some hunters also rely on hand-drawn maps that they, or other hunters, prepare. “Mental maps” are based on your memory of the direction and distances you have traveled. These should not be chosen over a good topographical map.

Using a Map and Compass A compass used alone is a valuable asset in unknown territory, but use it with an up-to-date, detailed map and a solid grasp of map and compass principles, and you have the next best thing to a local guide. Individually, a map and compass are valuable tools for navigation. Together they extend the limits of each, allowing us to determine the direction and distance to a destination and our ability to reach it. The distance from one point to another is determined by measuring the distance on the map using any unit of measurement. The metric system is the most convenient.

This measurement is then converted to the distance in the field by means of the map scale. For example, a measurement of 2 cm between two points on a 1:50,000 scale map would be equivalent to a distance of 100,000 cm or 1 km in the field. To find the direction or bearing between two pointson a map: 1. Draw a line between your starting point and your destination. (A - B) 2. Lay the baseplate edge of the compass along this line. Make sure the direction of travel arrow is pointing in the direction you wish to go. 3. Holding the compass base steady, turn the compass housing so the orienting lines in the compass housing are parallel with any meridian (North-South) lines on the map. Make sure that North on the compass housing is pointing toward North on the map. 4. Read the bearing on the compass housing at the base of the direction of travel arrow. Using the example in the figure below you would obtain a reading of 50°. Failure to comply with the statements above will result in an error of 180°. Second, most maps and their meridian lines are drawn according to true North. A correction for what is known as “declination” must be made. Check on the margin of the map to determine the angle of declination. In Eastern Canada the angle of Magnetic Declination is added to any bearings taken from the map. Depending on your location, your adjusted or magnetic bearing should be 18° to 30° greater in the Atlantic Provinces. Declination must be considered when using a map and compass to plot a course on the ground. Example: map bearing 50° + declination 23°W = magnetic (field) bearing 73°

MAGNETIC DECLINATION (VARIATION) The magnetic declination from true or map North is not the same in different places. It changes as you alter your position in relation to the north pole. Use the declination that is on the map you are using. This is the angle between true North (the direction of the north pole) and magnetic North (the direction of the magnetic pole, which is located roughly 2,300 km south, in the Boothia Peninsula of Nunavut). The reason declination decreases as you move West is that the magnetic needle need not swing as far off true North in order to line up with the magnetic pole. As you move West the declination decreases until it is nil. At that point, a line drawn North from your position would pass through both the magnetic North pole and the true North pole. In Canada this line of zero declination passes through the area of Thunder Bay, Ontario. East of this line, the declination is added to true bearings. West of this line it is subtracted. NOTE: The magnetic declination is given on each topographic map.

MAINTAINING A BEARING WHILE AVOIDING LARGE OBSTACLES To continue a journey along your compass bearing, when you come upon a large obstacle such as a body of water: 1. Pick a prominent landmark on the other side of the water that is in line with the intended course of travel. 2. Walk around the stillwater to that landmark, for example a large, dead tree, and continue from there on the original course. Upon reaching a barrier with no landmark on which to sight, “off-set” the compass at right angles to the direction of travel, (50° in the example provided). Swing left from 50° to 320° and, counting paces, walk along the new bearing to the farther end of the water. On reaching that position, swing back to 50° and travel in that direction to reach the other shore. Then place the compass on 140° and count the same number of paces back to the imaginary point where you would continue the old line of travel. Placing the compass on 50°, check the “back-bearing”, 230°, to see if it points to a previously chosen object at the place where you first came out to the water. If it does, then you know you will be continuing along the original line of travel when facing 50°. Practice with your compass before you go on your hunting trip. The time

to orient yourself using your compass, map, and landmarks is when you leave camp. If you wait until you are lost, it will be too late.