Wilderness Learning Center
Many emergency situations would not become survival situations, if you did not become lost. Many people carry compasses without knowing how to use them. The path of least resistance when traveling is usually the best. A map and compass can help you travel this way. Without direction, do you know where you are going in the woods, hills or mountains? Or how far you are from safety? Being lost in the short term causes fear, anxiety, rushing and making mistakes. Or in the long term, it can result in injury or death.
Let’s start with a map. Historically, highly accurate, detailed topographic maps have been developed for military use. They show the shape of the land in addition to other features. It looks interesting, but what do all the lines and symbols mean? The first place to study on a map is the Legend. Here you will find a scale to give you an idea it’s total area size measured in miles, kilometers and meters. It also includes contour intervals that give you a sense of elevation change, closer contour lines indicate steeper areas, farther apart means the area is flatter. There are common colors used on maps to designate land features: Blue shows water, black shows cultural, manmade features, brown represents earth topographic contours. Green shows vegetation and red shows land grids and important roads. Symbols for prominent features will vary per map. Map scales give you an idea of how large the area mapped is.
A standard USGS map at 1:24,000 means 1 of anything on a map (1” or 1 ‘) translates to 24,000 of the same thing in real life. Therefore, if 1” on a map is 24,000 “ in real life, 2.5” on the map will equal about a mile. A typical quadrangle map is 7.5 minutes latitude and 7.5 minute longitude. There is a variety of other marginal information on maps. For details see MapReading.com.
The earth is divided into 360 degrees of longitude (imaginary lines running North and South) They measure distance East to West. They are divided into 180 degrees East of the Prime Meridian and 180 degrees West of the Prime Meridian. There are 180 degrees of latitude with 90 north and 90 south of the equator running parallel and measuring distance North to South.
To prepare a map for use while traveling, first find the north arrows at the bottom of the map and use magnetic north for your navigation. Use a straight edge and draw magnetic north lines across the map parallel to each other. This will help you keep oriented even if the map’s magnetic north arrow happens to be folded out of view. Coat it with a map sealant or Thompson’s Water Seal. Fold carefully and store in a zip-lock bag for use. Carry it on your person, not in your pack, and have a spare map. If you are going into a specific area, you can photocopy it for easier use.
As you walk, you need to measure how far you have gone. Pacing is the traditional way. A true pace is a step with both your left and then right foot. Deriving from Roman times, 1000 paces was a Roman mile. The average pace of a Roman legion was 5.28 feet or 1/1000th of a mile. You will need to determine your individual pace factor by measuring how many paces it takes you to step out a given distance (1/10 of a mile). The formula to determine your factor is (Distance in feet divided by number of paces). Figure out how many paces it takes you to go 1/10th of a mile, if you add pace beads to your compass, have 4 (mile) beads separated from 9 (1/10th mile) additional ones. This way for every 1/10th mile you walk, pull down one of the 9 beads. When you have walked far enough to pull down a tenth bed, move one of the mile beads instead and return the nine to the other end of the string.
A compass is an instrument used for navigation and orientation that shows direction relative to the geographic cardinal directions (or points). Usually, a diagram called a compass rose shows the directions north, south, east, and west on the compass face as abbreviated initials. When the compass is used, the rose can be aligned with the corresponding geographic directions; for example, the “N” mark on the rose really points northward. Compasses often display markings for angles in degrees in addition to (or sometimes instead of) the rose. North corresponds to 0°, and the angles increase clockwise, so east is 90° degrees, south is 180°, and west is 270°. These numbers allow the compass to show azimuths or bearings, which are commonly stated in this notation. First invented in the Chinese Han Dynasty about 206 BC, and later adopted for navigation in the 11th century, the magnetic compass is the most familiar compass type. It functions as a pointer to “magnetic north”, the local magnetic meridian, because the magnetized needle at its heart aligns itself with the horizontal component of the Earth’s magnetic field. The magnetic field exerts a torque on the needle, pulling the North end or pole of the needle approximately toward the Earth’s North magnetic pole, and pulling the other toward the Earth’s South magnetic pole. The needle is mounted on a low-friction pivot point, in better compasses a jewel bearing, so it can turn easily. Modern needles are inside a capsule filled with a non-compressible under pressure liquid. Key points (N, S, E, W) and the needle point are often marked with luminous material to make them easier to read in low visibility situations. Magnetic north is about 1,000 miles from true north. A compass should be laid down on a level surface for the needle to work properly.
In order to express accurate direction, it is expressed in units of angular measure. The most common is the degree (º) with its subdivisions of minutes (‘) and seconds (“). 1 degree = 60 minutes; 1 minute = 6o seconds. To measure something, there always has to be a starting point, or zero (0) measurement and a point of reference. There are three baselines, one is true north (pointing to the North Pole), the second is magnetic north (direction indicated by the north seeking needle of a magnetic instrument), and the third is grid north (established using the vertical grid lines on the map and rarely used by the outdoorsman). Magnetic north is the one you should use for navigation with a compass. An azimuth is the horizontal angle measured clockwise from a north base line. and is used to express direction. The point from which the azimuth originates is the center of an imaginary circle, divided into 360 degrees. An azimuth can be measured from any of the three baselines.
Orienting a map means placing it on a surface and lining up magnetic north on the map with magnetic north on the compass. With bezel turned to 0 degrees north, place edge of compass on the magnetic north needle of the compass rose or one of the parallel lines you drew on the map. Without picking up the compass, turn the entire map with the compass on top until you put “red in the shed”. Your map is now oriented to the land.
To take a bearing (azimuth), first make sure your bezel is turned to 0 degrees north. Point the directional arrow on the compass toward the target destination. Notice where the magnetic north needle is pointed. Rotate the bezel until the north needle is “red in the shed”. When the needle is settled in the shed, read the bearing at the directional arrow. Walk to a prominent feature on the route and shoot your next bearing from there. If you have a map, you should measure the distance in paces from your starting point to ensure you don’t end up short or long.
Billie Nicholson, Editor