Have you ever reached a point on the path and become so confused that you’re not sure which way is up…or North?
A GPS is recommended on every outdoor adventure, but packing the backup methods like a compass can be the difference between reaching the middle of nowhere or the top of the world! This blog identifies the features to look for in a compass, details reverse polarity, and navigates the ins and outs of using a compass with topographic maps.
Follow our lead!
Ever reached a point on the path where you’re not sure which way is up? Credit: Suunto
How Does a Compass Work?
Fundamentally, a compass is a very simple piece of equipment. It consists of a permanent magnet rotating with minimal resistance about a central core. One marked end of the magnet points to the magnetic ‘north’ pole, and this information can be used for both navigation and orientating a map. The needle is mounted inside housing, and is situated on a baseplate.
Standard compasses just point ‘north’. However, an orienteering compass has degree markings that allow for taking bearings, therefore far more useful for navigation.
Why do I Need a Compass?
Let us guess: you’re lost? Keen to get out and explore the world?
Either way, the chances are that you’ll need a compass. It’s a simple and very useful piece of gear that is a must for navigation.
A compass helps with both finding where you are, and your way. This is useful, but also critical if you’re lost.
The main ways to use a compass are:
- ‘Setting’ the map with the compass so it aligns with what you see on the ground, and indicates that you’re heading in the right direction.
- Taking a bearing (direction) from the map and walking on that bearing.
- Using a bearing to identify features on the ground by checking the bearing from where you are.
- Identifying your own position using ‘back bearings’ from two or more distant known features (also known as ‘resectioning’).
A Basic Compass Should Be:
Easy to read and hold
It’s recommended not to buy a compass that is too small for you to accurately read or too large to fit either in your hands or in your pack.
Legible and accurate
For most applications, you need to either read or input bearings. Make sure the compass has legible bearing marks, and that they’re at a suitable interval for accurate measurements.
Most compasses have orientation lines and arrows to assist in orienting the compass, so make sure these are clear and legible too.
Finally, ensure the compass is tough.
Ensure your compass has legible bearing marks, and that they’re at a suitable interval for accurate measurements. Credit: Suunto
Features of a Compass
Generally, a basic orienteering compass is all you need to explore the great outdoors – however, some additional features can make navigation and route planning far simpler. There is a wide variety of compasses on the market, and each has a different set of features designed to suit different needs.
Most compasses feature the same as an all-time classic compass, like the Silva Ranger. Before using a compass to navigate, it’s recommended to become familiar with the main features:
This is usually a clear plastic base.
Also known as the compass wheel or dial. This has a mark preferably every two degrees (covering 360 degrees), and N-S-E-W (the ‘cardinal points’).
Red tip for ‘north’, white for ‘south’. In some cases, a black end indicates north.
Found on the bottom of the baseplate (also called ‘orienting lines’).
Fixed and aligned to ‘north’ within the compass housing.
The big arrow at the end of the baseplate.
Extension of the direction of the travel arrow.
The main working part of a compass is the magnetic ‘needle’ that floats on a central pivot. The red (or black) end always points to the earth’s magnetic north pole and the outer ring is marked with both the cardinal points of the compass (N-S-E-W) and every 2 degrees. These markings are used to attain bearings i.e. the direction from where you are to where you want to go.
If you rotate the ring (see second feature: ‘Compass Housing’) to align the red ‘north’ of the needle to the red arrow on the base plate, a bearing can be taken from the compass ring.
Generally, a basic orienteering compass is all you need to explore the great outdoors. Credit: Geordie Wright
There are many advanced features to look for in a compass that will improve the functionality too.
Some compasses feature a scale measurement along the edges. This allows for simple measurement of straight-line distances, without having to convert from measured units to the scale of the map. This can be particularly useful for road travel or four-wheel driving, where quick distance measurements are often required and the routes are generally straight.
If you are looking for a compass with a scale, ensure the scale on the compass aligns with the scale on the maps you use.
Magnifying lenses are often built into compasses. These can make reading small details on a map much easier. One would rarely carry a magnifying lens when navigating, however having one on your compass can be very convenient.
This can make navigation by bearings at night far simpler, negating the need to constantly turn your torch on and off. The only catch is that the compass only glows for a short time before it needs to be recharged by another light.
Tracing Markers and Offsets
Some compasses have markers for tracing, which can be useful for neatly marking up a map.
Another advanced feature is an offset. This allows the compass dial to offset to match true ‘north’ rather than magnetic ‘north’, having it easier to attain a bearing from a map with a magnetic offset. However, this can be confusing if you forget to re-set or adjust the compass when using a map with a different magnetic offset.
Where is North?
There is however, a slight complication; magnetic ‘north’ is not the same as map grid ‘north’, because magnetic ‘north’ (where the compass needle points) changes in different areas of the world, and also over time.
To achieve a completely accurate reading, you need to adjust the bearing to take account of the difference between map grid ‘north’ and magnetic ‘north’. The degree of deviation is marked on printed Ordnance Survey maps but, as a rough guide, you should adjust by 2 degrees by turning the compass housing anticlockwise. For longer trips, the difference can have a significant impact on navigation.
How to Use Your Compass
You may need the following items to help with carrying out the following steps:
- Topographic map (if you haven’t already got one in front of you while you’re scratching your head wondering ‘which way do I go?’)
- Pencil (ideally) or highlighter
The following step-by-step guide will make much more sense if you have the equipment listed above available to carry out each step as you go.
Line up the base plate edge with your direction of travel.
Lay your map somewhere flat and place your compass on top. Draw a line between your starting point and your destination to show the direction of travel. Then, align the baseplate edge with the direction in which you want to go, represented by the highlighted line on the map in the photo.
Rotate the graduated dial to line up with grid lines.
Keeping the baseplate edge of your compass in line with your direction of travel, carefully rotate the graduated dial until the ‘N’, orienting arrow (Compass Feature #5), and compass lines (Compass Feature #4) are all pointing in the direction of ‘north’ on your map. On most maps, ‘north’ is straight up, but make sure to check with the legend on the map you are using. Some maps do not adhere to this cartographic standard.
Ignore magnetic declination/variation for now – if accuracy is not critical, and the distance you have to travel is not enormous, you should be able to use the compass without declination/variation adjustment.
Line up the needle with north on the graduated dial.
Remove the compass from the map and hold it out level in front of you, with the direction-of-travel arrow (Compass Feature #7) pointing straight ahead. Turn your body until the north end of the magnetic needle (in this case, the red end, though it can be black as shown in other photographs) is directly over the orienting arrow, pointing to the ‘N’ on the dial.
The direction-of-travel arrow is now pointing in precisely the direction you want to travel to reach your destination.
The easiest way to use your compass now is by using the ‘snap or sight a line’ method: while holding your compass in the direction of travel, look up and sight a landmark or object that is not too far away but in the direction you want to travel. Put your compass away or hang it around your neck, and start walking towards your spotted/sighted landmark or object. Upon reaching it, repeat the process by holding your compass as before, ensuring it is still set according to your map. Continue this until you reach your destination. This is the method I find easiest and use the most, depending on the scenario.
Find Your Precise Position on a Map
Now that you know how to use a compass to navigate in the direction you want to travel, the next step is to learn how to determine exactly where you are along that path at any given point. This is another important use for a compass and another important lesson well worth learning before you head bush.
To determine your position, you will need to choose two landmarks easily identifiable on your map. Power lines, bends in rivers or streams, mountains, and lakes are perfect. Choose two that you can see from where you are standing, and mark them on your map as ‘L1’ and ‘L2’.
Holding the compass directly in front of you, point the direction-of-travel arrow toward the first landmark (‘L1’) and rotate the compass dial until the black end of the magnetic needle points to ‘N’ on the dial. Read the heading at the index line, which is the same as the direction of the travel arrow.
Pivot compass around landmark until orienting lines match map grid lines
Place the compass on your map with the baseplate edge touching the first landmark (‘L1’). Pivot the compass around on ‘L1’, until the orienting arrow or orienting lines align with the magnetic ‘north’ lines on your map.
Draw a line from the landmark (‘L1’) along the side of the baseplate across your map. Repeat this process for the second landmark (‘L2’) and your exact location is where the two lines intersect on your map.
The intersection of lines is your position.
At times, the old adage ‘trust your compass not the operator’ may no longer necessarily hold true. There have been reports of compasses suddenly developing “forced reverse polarity” and leading users into problems. Reverse polarity can not only be a nuisance, but life-threatening if you are using a compass in bad weather or during an emergency.
What is Reverse Polarity?
This happens when magnetic forces have affected the compass needle and forced it to reverse its polarity. Essentially, the ‘north’ end of the compass is pointing ‘south’, or thereabouts.
As modern-day campers, bushwalkers, paddlers, 4WD drivers, and outdoor enthusiasts – we are now surrounded by a plethora of ‘things’ that have a magnetic field. That could include mobile phones, radios, GPS, Personal Locator Beacons, cameras, car keys, tablets, cases for phones and tablets, hydration tube ‘clips’, and even the underwire of bras!
These are things we carry or wear while in the field. What about the shops with security wands, or certain things in the car that may affect us while we are travelling?
It would seem the biggest suspects in all of this are smart phones and cases with magnetic closures. How often do you jam your compass into the same pocket as your phone, or store them together in a pocket of your rucksack?
Reputable manufacturers such as Silva recognise this problem and suggest for users to check your compass every time they head out, as a survival safety step.
They can also repolarise your compass for you, while others suggest to simply do it yourself by swiping a magnet over the compass needle.
Avoiding Reversed Polarity:
- Store your compass away from any electronics you are carrying
- Hold your compass away from your body while using it
- Read your map and beware of what should be happening as you move forward on a bearing
- Carry a spare compass (safely stored) in case of a malfunction
- Check your compass before you leave home, and again before you start your trip
There You Have It!
Using a compass is relatively simple, and after you’ve attempted it the first time it only becomes easier.
It’s suggested to refresh your compass skills before heading off on any sort of adventure, to ensure you remain familiar with them.
Do you use or carry a compass with you on your adventures?
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