Using a Compass with Topographic map.
A compass and a map of the local area that you intend to use are two of the most useful tools that you can carry when on a hiking trip. It can mean the difference between an enjoyable trek in the woods or a nightmare made in hell. Imagine the anxiety being lost and not being able to find your way back to the vehicle or home. A cold wet night in the woods would not be enjoyable. Oh, and by the way, there is no cell phone signal to be had. There have been cases where an individual had been lost for several days and when found they were within 100 yards of their vehicle or camp.
Having a compass and a map is great, but are you sure you know how to use them correctly? I’ve met so many people that said sure, rotate the compass until the needle points north and travel accordingly. “Wrong!!!” Using a compass can be easy if you understand its parts and how they work together to get you to where you want to go. What I will try to attempt here is to outline the compass’ parts, the topographic map and how to couple the two together. Keep in mind that these two important pieces of equipment can be used independently.
First let’s take a look at the parts of the compass.
Not all compasses include each of these parts and some compasses include even more.
Each edge of a compass may have different rulers for use with different map scales
The baseplate is a hard flat surface on which the rest of the compass is mounted. It has rulers on its edges for measuring distances on maps. Its edge is straight and useful for laying lines on a map.
- Direction of travel arrow
The arrow is marked on the base plate that you point in the way you will be traveling.
The magnifier is for seeing small map features better.
- Index pointer
The butt end of the direction-of-travel arrow is where it ends at the edge of the dial. It is where you take degree readings.
The dial is a ring around the housing that has degree markings engraved on it. You hold the dial and rotate it to rotate the entire housing.
- Declination marks
These marks are used to orient the compass in an area with known declination.
- Orienting arrow
The arrow is marked on the floor of the housing. It rotates with the housing when the dial is turned. You use it to orient a compass to a map
- Orienting lines
These are a series of parallel lines marked on the floor of the housing and on the base plate.
The needle is a magnetized piece of metal that has one end painted red to indicate North. It sits on a fine point that is nearly friction less so it rotates freely when the compass is held fairly level and steady.
The housing is the main part of the compass. It is a round plastic container filled with liquid and has the compass needle inside.
A compass works by detecting the Earth's natural magnetic fields. ... This allows the needle to better react to nearby magnetic fields. Since opposites attract the southern pole of the needle is attracted to the Earth's natural magnetic north pole. This is how navigators are able to discern north.
Magnetism is one of the first bits of science we learn in school and just about the first thing we discover is that "like poles repel, unlike poles attract." In other words, if you hold two bar magnets so their north poles are almost touching, they'll push away from one another; if you turn one of the magnets around so one magnet's North Pole is near the other magnet's South Pole, the magnets will pull toward one another.
That's all there is to a compass: the red pointer in a compass (or the magnetized needle on your home-made compass) is a magnet and it's being attracted by Earth's own magnetism (sometimes called the geomagnetic field—"geo" simply means Earth). As English scientist William Gilbert explained about 400 years ago, Earth behaves like a giant bar magnet with one pole up in the Arctic (near the North Pole) and another pole down in Antarctica (near the South Pole). Now if the needle in your compass is pointing north, that means it's being attracted (pulled toward) something near Earth's North Pole. Since unlike poles attract, the thing your compass is being attracted to must be a magnetic South Pole. In other words, the thing we call Earth's magnetic north pole is actually the South Pole of the magnet inside Earth. That's quite a confusing idea, but it'll make sense if you always remember that unlike poles attract.
Earth's magnetic field is actually quite weak compared to the "macho" forces like gravity and friction that really dominate our lives. For a compass to be able to show up the relatively tiny effects of Earth's magnetism, we have to minimize the effects of these other forces. That's why compass needles are lightweight (so gravity has less effect on them) and mounted on friction less bearings (so there's less frictional resistance for the magnetic force to overcome).
Learning the Basics
Hold the compass correctly. Place the compass flat on your palm and your palm in front of your chest. This is the proper compass stance, when traveling. If you're consulting a map, place the map on a flat surface and place the compass on the map to get a more accurate reading.
Find out where you're facing. For a quick basic exercise to orient yourself, it's good to find out which direction you're currently facing or traveling. Look at the magnetic needle. It should swing off to one side or another, unless you're facing north.
- Turn the degree dial until the orienting arrow lines up with the magnetic arrow, pointing them both North, and then find the general direction you're facing by looking at the direction of travel arrow. If the direction of travel arrow is now between the N and the E, say, you're facing northeast.
- Find where the direction of travel arrow intersects with the degree dial. To take a more accurate reading, look closely at the degree markers on the compass. If it intersects at 23, you're facing 23 degrees northeast.
Magnetic North vs. True North
Understand the difference between "true" North and "magnetic" North. While it might seem confusing that there are two kinds of "North," it's a basic distinction that you can learn quickly, and it's an essential piece of information to learn to use a compass properly.
- True North or Map North refers to the point at which all longitudinal lines meet on the map, at the North Pole. All maps are laid out the same, with True North at the top of the map. Unfortunately, because of slight variations in the magnetic field, your compass won't point to True North, it'll point to Magnetic North.
- Magnetic North refers to the tilt of the magnetic field, about eleven degrees from the tilt of the Earth's axis, making the difference between True North and Magnetic North different by as many as 20 degrees in some places. Depending where you are on the surface of the Earth, you'll have to account for the Magnetic shift to get an accurate reading.
- While the difference may seem incidental, traveling just one degree off for the distance of a mile will have you about 100 feet (30.5 m) off track. Think of how off you'll be after ten or twenty miles. It's important to compensate by taking the declination into account.
Learn to correct for declination. Declination refers to the amount by which North on your map and North on your compass differ at any given point, given the Earth's magnetic field. To make using the compass much easier, you can correct for declination by either adding or subtracting the declination amount from your bearing in degrees, 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.
- In the US, the line of zero declination runs up through Alabama, Illinois, and Wisconsin, at a slight diagonal. East of that line, declination orients toward the West, meaning that Magnetic North is several degrees West of True North. West of that line, the opposite is true. Find out the declination in the area in which you'll be traveling so you can compensate for it.
- Say you take a bearing on your compass in an area with West declination. You'll add the number of degrees necessary to get the correct corresponding bearing on your map. In an area with East declination, you'll subtract. Below is a handy calculator to determine your particular area of travel.
Gather your bearings to find out which direction you're headed. When you're hiking around in the woods or in the field, it's good to periodically check your bearings to make sure you're going in the direction you intend. To do this, move the compass until the direction of travel arrow is pointing in the direction you've been traveling and will continue traveling. Unless you’re heading north, the magnetic needle will spin off to one side.
- Twist the degree dial until the orienting arrow lines up with the north end of the magnetic needle. Once they're aligned, this will tell you where your direction of travel arrow is pointing.
- Take off local magnetic variation by twisting the degree dial the correct number of degrees to the left or right, depending on the declination. See where the direction of travel arrow lines up with the degree dial.
Continue moving in this direction. To do so, simply hold the compass in the proper stance, turn your body until the north end of the magnetic needle once again aligns with the orienting needle, and follow the direction of travel arrow. Check your compass as often as you need to, but be sure not to accidentally twist the degree dial from its current position.
Focus on points in the distance. To accurately follow the direction of travel arrow, look down at the arrow, then focus on a distant object like a tree, telephone pole, or other landmark, and use this as a guide. Don’t focus on anything too distant, like a mountain, as huge objects aren’t precise enough to navigate by accurately. Once you reach each guide point, use your compass to find another.
- If visibility is limited and you cannot see any distant objects, use another member of your walking party (if applicable). Stand still, and then ask them to walk away from you in the direction indicated by the direction of travel arrow. Call out to them to correct their direction as they walk. When they approach the edge of visibility, ask them to wait until you catch up. Repeat as necessary.
Using the Compass with a Map
Transpose the direction of travel onto your map. Place your map on a horizontal surface, and then place the compass on the map so that the orienting arrow points to true north on the map. If you know your current position on the map, slide your compass around so that its edge passes through your current position, but its orienting arrow continues to point north.
- Draw a line along the compass edge and through your current position. If you maintain this bearing, your path from your current position will be along the line you just drew on your map.
Learn to take a bearing from the map. To find out which direction you need to travel to get somewhere, place the map on a horizontal surface and place your compass on the map. Using the edge of the compass as a ruler, place it so that it creates a line between your current position and where you intend to go.
- Rotate the degree dial until the orienting arrow points to true north on the map. This will also align the compass’s orienting lines with the map’s north-south lines. Once the degree dial is in place, put the map away.
- In this case, you'll correct for declination by adding the appropriate number of degrees in areas with West declination, and subtracting in areas with East declination. This is the opposite of what you'll do when first taking your bearing from the compass, making this an important distinction.
Use the new bearing to navigate. Hold the compass horizontally in front of you with the direction of travel arrow pointing away from you. Use this arrow to guide you to your destination. Turn your body until the north end of the magnetic needle is aligned with the orienting needle, and you'll be properly oriented toward the destination on the map.
Finding Your Bearings When You’re Lost
Choose three prominent landmarks that you can both see and find them on your map. One of the most difficult and advanced things you can do with a compass, but one of the most important, is finding out where you are when you don't know your exact location on the map. By locating distinctive landmarks you can see on your map, ideally as widely spread around your field of view as possible, you can get yourself re-oriented.
Aim the direction of travel arrow at the first landmark. Unless the landmark is north of you, the magnetic needle will spin off to one side. Twist the degree dial until the orienting arrow lines up with the north end of the magnetic needle. Once they are aligned, this will tell you where your direction of travel arrow is pointing. Correct for declination, for your area.
Transpose the direction of the landmark onto your map. Place your map on a horizontal surface and then place the compass on the map so that the orienting arrow points to true north on the map. Then, slide your compass around so that its edge passes through the landmark on the map, while the orienting arrow continues to point north.
Triangulate your position. Draw a line along the compass' edge and through your approximate position. This is the first of three lines you will draw to find your position by forming a triangle with the other two landmarks.
Repeat this process for the other two landmarks. When you’re done, you will have three lines that form a triangle on your map. Your position is inside this triangle, the size of which depends on the accuracy of your bearings. More accurate bearings reduce the size of the triangle and, with lots of practice; you may get the lines to intersect at one point.
Additional Information for using compass and the map courtesy of SUUNTO
First, you need to determine your bearing (the direction you need to travel). Use the following procedure to obtain an exact travel direction towards your desired destination. The procedure will work if the magnetic North-South lines are drawn on the map.
1 a) Place the compass on the map so that the long edge connects the starting point with the desired destination.
2 a) Hold the compass firm on the map in order to keep the base plate steady.
3 a) Hold the compass in your hand in front of you. Make sure that the base plate is in horizontal position and that the direction arrows are pointing straight ahead.
Tip 1: Now that you have determined your necessary bearing, you need to make sure you maintain an accurate bearing. First, you should find a suitable target in the terrain (e.g., a tree, boulder or a bush) towards which the direction arrows point. Walk towards the chosen object without looking at your compass. When you reach your target, find a new object that is aligned with your bearing, and repeat the process.
Tip 2: Sometimes the compass capsule may get turned accidentally while you are walking. Remember to check from time to time that the capsule has not deviated from the direction that had been set on the compass.
Tip 3: Remember the difference between the magnetic needle that always points to the magnetic North Pole and the direction arrows that show the travel direction.
A special thanks to Suunto for providing the content for this useful page.