Using a compass in the outdoors is central to a lot of activities from hill walking, cycling and camping.
They are light weight and take up little space, yet are very dependable and when used in conjunction with and Ordnance Survey map, will ensure you find your way to your destination. With the information on this page, we aim to show you how to correctly use a compass. The first thing we’ll start with is identifying the various parts on a compass.
All compasses include many common features.
- Baseplate – the plastic rectangular transparent base.
- Compass housing or wheel, degrees covering 360 degrees, and N-S-E-W or cardinal points for North, South, East and West.
- Magnetic needle – red end for north, black end for south.
- Compass lines or orienteering lines – on the bottom of the compass housing.
- Orienting arrow (2 green lines on this compass) – fixed and aligned to north within the compass housing.
- Index line – the beginning of the direction of travel arrow.
- Direction of travel arrow – the arrow at the end of the baseplate.
- Map scales 1:25 000, 1:50 000 and metric measurer or Romer scales.
How to use a compass is a technique which is quick to learn and can be put to use no matter where you are.
A Compass can be used for the following
A compass can assist you to locate where you are and how to get to another point. While many believe a Sat Nav or Smart Phone app will do this job for them, it must be borne in mind that electronic instruments can fail, break or run out of power.
- Aligning the map with the compass so that your location matches what you see on the ground, and that you’re heading in the right direction.
- Taking a bearing (direction) from the map and walking.
- Using a bearing to identify features coincident on the ground and map.
- Use ‘back bearings’ to identify where you are from two or more distant known objects.
Magnetic North and True North
Magnetic north is different to map grid north because magnetic north (where the compass needle points) changes in different places of the world and changes over time. The longer your trip the greater the variance between the two.
You have to adjust the bearing on the compass to take account of the difference between map grid north and magnetic north. The difference in degrees is marked on printed Ordnance Survey Ireland maps but as a rule of thumb, adjust by 5 degrees by turning the compass housing anticlockwise.
Which way do I go?
To figure out which way you need to go to reach your destination, you will need to know where you are and where that is on the map. Then identify on the map your destination. Following that…
- Place the edge of the compass base plate along the line connecting A. where you are and B. your destination.
- Rotate the compass housing so that the parallel lines contained within, line up with south/north grid lines on the map.
- Take the compass and place close to your body and rotate yourself where you stand until the north end of the compass needle aligns with N in the compass housing.
- Follow the directional arrow which will be pointing away from you and identify a point in the distance
- Travel to the point identified and repeat the process when you get there.
