How to Use a Compass
A compass is an essential piece of kit for use with OS maps when navigating through the countryside. Getting to grips with handling and using a compass can sometimes be confusing.
Learning how to use a compass is a skill that everyone who enjoys the outdoors will find useful and can be essential if you walk in isolated areas or in more challenging conditions.
To navigate successfully you will need to use your compass alongside a map – so first make sure you are comfortable with reading maps first. In urban areas and lowland countryside in good visibility, good map readers can navigate well without using a compass.
For walking we recommend an orienteering compass with a rectangular base (like the below), which is marked with km/m scales that can be seen even in poor light.
Uses of a compass
A compass helps you to:
- Know which direction you are travelling in – this is called your heading
- Align or orientate your map with your surroundings – setting the map
- Work out which direction an object or destination is from you – its bearing
- Follow a straight line of travel – called following a bearing
Main features of a compass
- Baseplate - the plastic base
- Compass dial - also known as the compass wheel, with a mark every two degrees covering 360 degrees, and the four main compass points N-S-E-W
- Magnetic needle - red end for north, white for south
- Compass lines - on the bottom of the base. These are also called ‘orienting lines’
- Orienting arrow - fixed and aligned to north within the dial
- Index line - extension of the direction of travel arrow
- Direction of travel arrow - the big arrow at the end of the baseplate
- Map scales 1:25 000, 1:50 000 and metric measurer (known as Romer scales)
The key thing about the compass is that the needle always points to magnetic north. This is slightly different from grid north, and the difference between them varies in different areas of the world and over time. Information about this ‘magnetic declination’ is usually printed on walkers’ maps. Over short distances it should make little difference to your navigation but if you are walking on a single bearing for a very long distance in open countryside you need to compensate for it in order to navigate accurately.
Checking your heading
- Hold the compass in front of you with the direction of travel arrow pointing in the direction you’re walking
- Rotate the dial so that the N aligns with the red end of the compass needle
- The figure on the rim of the housing at the index line is your heading
Setting the map
An excellent use of a compass is to help you set the map, aligning it so that it corresponds to the surrounding landscape. This makes it much easier to relate the map to what you see on the ground.
- Put the map as flat as possible in front of you
- Put the compass anywhere on the map
- Turn the map and compass until the needle on the compass aligns with the north-south gridlines on the map, with the red needle pointing to the top of the map
Following a bearing
- Find a distant feature on the map that you want to walk towards
- Identify this feature on the ground
- Put the compass on the map so that orienting lines on the compass point line up with your route towards that feature, as it is shown on the map
- Without moving the map or compass, rotate the dial so that the orienting arrow points towards north on the map - the figure on the rim of the housing at the index line is the bearing you need to follow
- Take the compass off the map and hold it with the direction of travel arrow pointing straight ahead away from you
- Rotate your whole body, including the compass, until the red end of the needle lies parallel with the orienting arrow
- The direction of travel arrow should now point towards your distant feature
- Walk in the direction indicated by the direction of travel arrow until you reach your destination, checking your bearing along the way
The same technique can also be used to check the direction of a path on the ground after taking its bearing from the map.
Advanced techniques include using a map and compass with a pencil to locate your exact position by taking bearings from two or more distant landmarks, known as resectioning.