In the hands of a trained individual, a compass becomes an invaluable tool to the one who wields it. Whether it’s used to plot a path from point A to point B, determine what quadrant you’re located in, or locate your approximate position on a typographical map when you aren’t sure where you are, the importance of having and knowing how to use a compass will never be overshadowed by the technological marvels of global positioning satellite (GPS) devices when the technology fails.
What is a compass?
A compass is a simple device which contains “a magnetized metal needle that floats on a pivot point.” This needle always points to the northern magnetic field of the earth. It’s important for you to remember this critical point because the magnetic field of the earth is constantly changing, so any time you need to use a compass, you’re going to have to account for a difference between the compasses (magnetic) north, and the true (polar) north. This difference is known as the declination variance.
All typographical maps that are commonly used with a compass out in the wild are imprinted with the declination variance when the map is made. To be sure that you have the most current declination variance for any area you plan to traverse with a compass, you can contact the National Geophysical Data Center (NGDC) for the information.
Due to subtle differences in various compass designs, a mountaineer’s compass is used as the basis for these instructions.
The first compass bearing you need to learn is how to get from point A to point B.
1. Mark your starting location on your typographical map, and then place a mark at your destination. Using a ruler or other straight edge, draw a straight line from your starting point to your destination.
2. Place your compass on the map so that the center of it is directly over, and in-line with your line between points A and B.
3. Rotate the dial on the compass housing so that the large red arrow points to the north on your map, and the smaller lines within the housing are parallel to the map’s grid lines that point north.
4. Take a look at the mark on your dial that’s in-line with your direction of travel. This is your relative directional bearing.
5. The next thing you need to do is to take the magnetic declination variance and adjust your bearing accordingly.
6. On your typographical map you’ll find a small diagram with the letters “MN” for magnetic north listed on it, and just below the “MN” will be an arrow and a number. This number is the magnetic declination variance that needs to be calculated into your bearing. If the “MN” arrow is to the left of the true north line, add the declination value to your bearing; if the arrow is to the right of the true north line, subtract the value and adjust your compass bearing on the compass dial. If you’re using an older map, use the declination value you obtained from the National Geophysical Data Center when you make the final grid bearing calculation. Failure to do so could put you thousands of feet, or miles from your intended destination.
7. While holding your compass in front of you, pointed in the direction of travel, rotate your body until the red magnetic arrow pointer is inside the large red arrow. You’re now ready to start hiking to point B. Refer to your compass often to keep you on track and you shouldn’t have any difficulty finding your way to your final destination.
The second compass bearing you need to know is called a “triangulation bearing.” In the event you should become lost and need to find out where you are, you can use your map and compass to determine your approximate position, based on landmarks you can see with your eyes and identify on your map.
1. Take out your map and orient it with your compass.
2. Scan the area around you to locate at least two distinct landmarks that are approximately 90 degrees apart.
3. Locate the first landmark on your map.
4. Move your compass so that one of the long straight edges points towards the first landmark while ensuring that both the orienting arrow and magnetic needle in the dial of the compass point to north on your map.
5. Draw a line from the landmark down the length of the compass baseplate.
6. Repeat this same procedure for the second landmark you identified.
7. Your approximate position is where both of these lines intersect on your map.
To be more accurate, you can select a third prominent landmark for your triangulation bearing, but two landmarks will normally be sufficient to determine your approximate position.
In the event that you should notice something out of the ordinary while on your adventures in the wild, and you feel it may be important to report it to law enforcement or park authorities, there is a third compass bearing you can take that will provide them with a basic area that needs to be checked out.
This third compass bearing is known as a “quadrant bearing”, and is based on how people normally give directions such as north, east, south and west. When you relate these directions to a compass dial the resulting degree angles would look like the example below.
Example: north (N) = 0, east (E) = 90, south (S) = 0, west (W) = 90
Let’s say for example you’re hiking across the top of a hill and when you pause for a moment to take a break, you notice the wreckage of what appears to be some kind of aircraft way off in the distance. This is something important that needs to be reported so you take a triangulation bearing to determine approximately where you are. You’re headed in a northerly direction, but the wreckage is slightly behind you towards the southeast.
How are you going to tell them where the wreckage is, approximately?
1. Orient a compass to your map with the declination variance included.
2. With the compass in hand, take a bearing to the object and write it down.
If the bearing you took was in a direction of 120 degrees. This bearing is closer to south than it is to north. What you do now is you count the total number of degree marks there are between the “S” mark on your compass and the 120 degree mark, which in this example is equal to 60 degrees.
To report this correctly you would write “S 60 E” which is saying the object you’re reporting is in the southern quadrant 60 degrees to the east. If the bearing you had taken was in the northern quadrant at 17 degrees you would report it as “N 17 E” which equates to the northern quadrant 17 degrees to the east. If these bearings were in the western quadrants, they would be reported as “S 60 W” and “N 17 W” respectively.
What if a quadrant bearing is directly north, south, east, or west?
You would report them as due north, due south, due east or due west respectively from your map position.
Understanding how to use a compass in relationship to a typographical map and the magnetic field of the earth is critical to being able to navigate through the wilderness accurately without becoming lost. By learning how to use a compass, and practicing with it under controlled conditions, when you do finally arrive at the moment you have to use your land navigation skills in a real-world environment, you can rest assured that you’ll do it right to stay out of harms way.