A compass is part of the most essential gear that you take into the backcountry. It’s also valuable as an emergency survival tool anywhere.
Although it’s a basic tool for navigation on land or water, a compass can look intimidating at first. Learning a few basics will make it easy for you to confidently navigate in wilderness areas or other public lands. All the basic techniques are spelled out here, and they’ll be especially easy to absorb if you’ve got a compass in front of you.
The first thing to do is get familiar with the parts of the compass, what the different lines are, what parts of it turn and why. Keep in mind that not all compasses have all of these parts, but each of these features does make it easier to get full use of the compass. We’ll focus on the kind called a baseplate compass, which is the one most commonly used in the field; it will have all these parts.
(If instead you have a lensatic compass, you’ll have a sighting wire and a rear lens. These make it possible to take very accurate bearings, but also make this type of compass a bit more challenging to get used to.)
Parts of a Compass
- Baseplate: A transparent surface that you can see through when you set it down on top of your map.
- Straight Edge: A feature along the sides of the baseplate, which you’ll use for taking bearings. Along the side are rulers to help you calculate the distance in accordance with your map’s scale.
- Direction-of-Travel Arrow: The little arrow on the baseplate that points away from the compass. It tells you which way to walk, once you have positioned the compass properly. You can also point it at a landmark and then take a bearing of that landmark.
- Compass Housing: The clear plastic housing the magnetized needle.
- Rotating Bezel: A dial marked with degrees from 0 clockwise to 360 (also called an azimuth ring).
- Index Line: A line that extends the direction-of-travel arrow and shows you where to take bearings.
- Magnetized Needle: The needle that floats on a pivot point. The red end always points toward the magnetic north.
- Orienting Arrow: The non-magnetic arrow used to help you orient the bezel.
- Orienting Lines: Markings used to line up the compass with north on your map.
Some compasses have a declination scale to make it easier to adjust declination.
Others have a sighting mirror that makes it easier to take accurate bearings because you can see both the landmark you’re measuring and the bezel at the same time.
True North vs. Magnetic North
True north is a fixed point that never changes. It is the north end of the imaginary line around which the earth rotates. When we talk about the North Pole, we’re referring to true north.
However, because of fluid movements in the earth’s core, our planet’s magnetic field is continually shifting. That means the magnetic poles move every year. During the 20th century alone, the Magnetic North Pole has moved 680 miles (1,100 km), and in the last 50 years, it has moved faster and faster, accelerated from 5.6 miles (9 km) to 32.3 miles (52 km) each year. Interestingly, the Magnetic South Pole is also constantly moving, but the two do not line up exactly opposite each other across the globe. Earth’s magnetic field isn’t shaped with perfect symmetry.
The needle in a compass will always point to magnetic north, which is somewhere in northern Canada right now, about 800 miles from the True North Pole. Right now, magnetic north is about 11 degrees different from the tilt of the earth’s axis. If you looked at your compass needle and confuse its aim (magnetic north) with true north, you’d head in the wrong direction. If you’re just one degree off, walking for a mile in that direction will land you 100 feet off. Walking ten miles will put you way off! So, resetting your compass so that the magnetized needle points to true north will make life easier – and get you where you’re going.
Declination is the angle difference between true north and magnetic north. In other words, declination describes the amount by which north on your map and north on your compass differ from each other, given the Earth’s magnetic field. To correct for declination, either add or subtract the declination amount from your bearing, depending on whether you’re taking a bearing from a map or from your compass, and whether or not you’re in an area with east declination or west declination.
Depending on where you are in the world, the declination will be a certain number of degrees to the east or west. In the US, the line of zero declination threads diagonally up through Alabama, Illinois, and Wisconsin. If you’re east of that line, declination orients toward the west, meaning that magnetic north is several degrees west of true north. When you’re west of that line, it’s the opposite.
Mapmakers align their maps to true north, but on topographic maps, there is usually an indication of the declination appropriate to the region shown in that map. The declination diagram is near or inside the legend on a map, and the best maps also state the date they were updated, because declination changes over time. If your map wasn’t recently updated, it’s worth checking the current declination online as you prepare for your journey.
Once you know your declination, subtract it from your compass bearing for west, or add it for east. Setting the declination might involve turning a little screw in the back of the housing. Different brands of compasses will have different mechanisms for setting declination. When you’ve set the declination on your compass and turn it so that the magnetized needle lines up inside the orienting arrow, the mark on the bezel that says “N” will point to true north.
How to Take a Bearing From a Map to Find an Object in the Field.
A bearing (also called a heading) describes a direction. It’s much more precise than saying, “walk east to get to the lake.” Instead, you might say “follow a bearing of 84 degrees to reach the lake.”
Let’s say you want to head to a specific spot you see on your map. Place the compass on the map in such a way that the straight edge of the compass’s baseplate forms a line connecting your current location with your destination. Or, if the baseplate isn’t big enough, draw a line connecting location to destination, and line up the edge of your compass on this line so that the travel arrow points in the direction you want to travel.
Next, rotate the bezel until north on the map and the orienting lines on the compass are aligned. (It doesn’t matter which way your map is actually facing in the world, because you aren’t using the magnetized needle for anything – yet!) When you remove your compass from the map, it will keep that bearing you’ve just captured – you can read the number if you like. Turn your body until the north end of the magnetized needle is inside the orienting arrow. You can remember to put “Red in the Shed.” Once you’ve got the needle inside the orienting arrow, you’re facing the right way.
Hold the compass with the direction of travel arrow pointing away from you, and you can start on your way.
Focus on points in the distance: To accurately follow the direction of travel arrow, look down at the arrow, then transfer your focus to a distant object like a tree or other landmark, and use this landmark as a guide. Don’t choose something too far away or too big, like a mountain, as huge objects aren’t precise enough to navigate by. Once you reach each guide point, use your compass to find another.
Simple techniques for traveling by sight: If you can already see your destination, a compass can still help you reach it during the moments you may lose sight of it. If you are heading to a mountain for example, point at it from your current position with the travel arrow on the compass. Then rotate your azimuth ring until the orienting arrow is lined up with the red end of the magnetic needle pointing towards the north. Continue on your path so that the needle and its housing remain intact and you should have no problem reaching your destination.
How to Take a Bearing in the Field to Find Where You Are on a Map
It’s a more complicated process, but one of the most important things a compass can do for you is help you get your own bearings when you’re lost.
First, you’ll choose two or three landmarks that you can see around you, spaced out widely in your field of vision. Two will work but three is even better. You might use the spur of a mountain, a lake – anything that you can also find on your map. You’ll take a bearing off these objects and then using it to figure out where you are.
Hold your compass up with the direction of travel arrow pointing directly at that landmark. Next, rotate your bezel until the magnetized needle is inside the orienting arrow (“red is in the shed”). Once you measure that bearing, you have to transfer it to your map.
Lay the compass down flat on your map. Make sure the direction of travel arrow is pointing at the landmark on the map, and the edge of the compass touches that landmark. Rotate the entire compass until the orienting lines on the compass line up with the north-south grid on the map, and draw a line along the edge of the baseplate. The line should go through the landmark.
Once you have that first line drawn, repeat the process with a second landmark. You are situated close to where those two lines cross on the map. If you have found a third landmark, you’ll have even more information. The three lines you draw will form a little triangle, which is why this process is called triangulating. You are somewhere inside that triangle. The more precise you are, the smaller the triangle. With practice, you can get the three lines to intersect at one point. That is your location.
Now that you’ve read about how things work, it’s time to get outside and try it! This is a skill that’s easiest to learn by doing. You can practice anywhere before heading into the backcountry.
Many airplanes and ships carry a compass even today, as do casual boaters and hikers. Your phone also can have a compass app in it that does not need to be connected to the internet to function – but it will need a charged battery. So for any extended time away from a power source, the real thing is a must-have!
Why isn’t my compass needle pointing north?
You may have placed it close to a metal object, which can attract the magnetized needle and distract it from north. Iron and steel will both do this.
Why is my compass stuck?
Make sure you’re holding it absolutely level, or the magnetized needle may drag on its own housing. If when it’s level it still won’t move, try tilting it very slowly until the needle swings free. You may have a compass with a weighted needle, purposely weighted on one end. Depending on where you are in the world, it will need to be slightly tilted to compensate.
My compass has a bubble in it, is that okay?
Yes. You can use that bubble to make sure your compass is level.
Will a compass I buy in the northern hemisphere also work in the southern hemisphere?
Yes. Your compass’s needle will still point north.