There are three basic skills to using a compass proficiently. These are setting the map, taking a bearing and walking on a bearing. Let’s detail each of them:
Setting the map
Correctly position your map to reflect what you can visibly see will help you walk on a bearing when you can’t sight your destination. Using a compass to do this can be done in four easy steps:
1. Turn the compass housing until the index pointer is aligned with the value for magnetic variation (or declination) printed on your map.
2. Position the ‘direction of travel’ arrow along a vertical grid line so that it points towards the top edge of the map.
3. Rotate the map and compass in this position until the compass needle points to the north.
4. Double check the alignment is correct by identifying and matching actual land features to their representations on the map.
Taking a bearing
Finding the angle from north to the direction of your destination so that you have a fixed reference. This is the method to use if you can’t sight your destination.
1. Hold the compass flat in your hand with the direction of travel arrow pointing towards your destination for the current leg of your journey.
2. Turn the compass housing until the compass needle lines up over the orienting arrow. Make sure you are using the needle’s north pole (usually marked red). Check your compass instructions if you’re unsure.
3. Read the value in degrees from the index pointer mark on the compass housing to the orienting arrow. This is your bearing. Keep the housing in this position.
4. Check your bearing regularly by aligning the compass needle with the orienting arrow to make sure you’re following the direction of travel arrow.
Practice this procedure repeatedly at home until you’re completely familiar with it. Mistakes when hiking can cost you valuable time and energy.
Walking on a bearing
Setting your compass to a known bearing to determine the direction of travel. Use this method if you can sight your destination when taking your bearing.
1. Turn the housing of the compass until the index pointer aligns with your bearing.
2. Turn the compass until the needle is positioned over the orienting arrow.
3. Choose a landmark along your line of travel and head towards it.
4. Once you reach a marker, choose another. Check your bearing regularly.
It’s important to always take a bearing before beginning your journey, even if you think you’ll be able to see your destination the whole time. Despite a seemingly favorable lay of the land, terrain can change unexpectedly and so can weather conditions. You may take longer to reach your destination for the day than anticipated and need to walk after dark. Having a compass bearing greatly reduces the risk of disorientation under these circumstances.
Combining a map and compass when walking on a bearing increases the accuracy of navigation but involves converting bearings from map to field. To do this add the magnetic variation to your grid bearing by turning the compass housing anti-clockwise. For example, if your grid bearing is 136 degrees and magnetic variation is 5 degrees, you would turn your compass housing to the left to set it to an adjusted bearing of 141 degrees. Converting a magnetic bearing to grid bearing is the reverse process.
However, the procedure as described here is only true for locations where the magnetic variation is west of true north, as in the UK. For location east of true north, you would need to subtract the variation value by turning the compass housing to the right.
Finally here are a few important tips to bear in mind when navigating using a map and compass:
1. Remember to allow for the magnetic variation at your location. For every kilometer you travel without having adjusted your bearing according to the magnetic variation, you could be 100 meters or more of course. After a 20 km hike, that’s a fair distance, and you could be arriving at your destination in the dark.
2. Be aware of objects around you that may magnetically interfere with your compass. Wire fences, railway lines, rocks (they can contain trace iron) and even personal items like watches and belt buckles can cause your compass to give inaccurate readings. Over longer distances, even slight intereferences can translate to a large error at the destination.
3. Make sure the orienting arrow is pointing to the top of the map. If it’s the wrong way round, then so will you be (i.e. heading in the opposite direction than you should).
4. Make sure the direction of travel arrow is pointing from start to finish. Otherwise, you’ll be walking the wrong way. This is a surprisingly common mistake.