In this tutorial, we will go through 2 simple exercises. The first will be taking a bearing from a map to show you the direction of travel on the ground and the second exercise will be to taking a bearing in the field to know your location on the map.
Before we start with any of the exercises, we need to adjust our compass for magnetic declination.
Magnetic declination is the variation angle between true north and magnetic north, noting that all compasses always show magnetic north while north shown on the maps is the true north.
To adjust this declination, turn over your compass, and with the small key attached to the compass string turn the small screw found on the back of the rotating bezel up to the desired degrees East or West.
Most maps will feature a magnetic declination diagram showing the declination at a certain point in time (like the one illustrated here in), so it is of absolute necessity to check the date the map was printed. In addition to the magnetic declination diagram, the map will also show the annual variation (otherwise you can check the declination online).
If the magnetic declination is 5 degrees East, then rotate the adjustment screw to read 5 degrees towards East on the declination scale. Rotate the compass until you get the north side of the magnetized needle inside the orienting arrow – what is commonly called “Red in the shed”. Once that is done, the north mark on your bezel will now point to true north.
After the adjustment, you will not need to worry about declination until you move to another area.
Now back to our main exercises.
Exercise #1: How to determine the direction of travel on the ground:
1. Taking a bearing from a map:
Bearing describes a direction in terms of degrees.
For this exercise to be relevant, you need to be aware of your location on the map (Point A) and the point of destination on the map (Point B).
Put your map on a leveled surface, then put your compass on the map . Rotate the compass to align Pt A and Pt B, with the travel arrow (shown in picture above) pointing towards your destination (Pt B). Now rotate the bezel on your compass, so that the orienting lines are parallel to the North and South of the map (Make sure the north sign of the bezel is towards the same direction of the north on the map. Look at the index line to read the bearing (in degrees).
2. Using the compass to follow a bearing in the field:
Hold the compass in front of you, directing the travel arrow away from you. Rotate your body until the North side of the magnetic needle is inside the orienting arrow “Red in the shed”.
Once you get to the “Red in the shed”, it means you are facing your bearing and your destination.
Exercise #2: How to know your location on the map:
1. Taking a bearing in the field:
Identify a landmark in the field that you can identify on the map.
Hold your compass with the travel arrow directed away from you towards the landmark.
Keep the compass still & flat, then rotate the bezel until you get the Red in the shed.
Look at the index line to read the bearing.
2. Using the bearing to locate yourself on the map:
Lay your compass on the map with the edge close to the landmark.
Rotate the whole compass until orienting lines are parallel to the North and south of the map (The north mark o n the bezel should be in the same direction as the north on the map).
Once done, draw a line on the map , your location is somewhere on the line.
To know your exact location, you need to use a process called triangulation, consisting of repeating the same exercise 2 additional times with 2 different landmarks. Now that you have 3 drawn lines, you will notice that they will form a triangle, you are somewhere inside this triangle, the smaller the triangle the more accurate you are in determining your location on the map.
