I've been an active Search & Rescue volunteer since 2007 with the Coconino County Sheriff's SAR Team in northern Arizona.
Don't Get Misplaced While Navigating in the Backcountry
Know Your Map and Compass Skills
I can't say there's just one thing you should never go without when heading into the backcountry—in fact, I have a whole list of what I consider essential gear—but a map could be in the top spot on that list and a compass is a close second.
A map is a crucial tool for accurate navigation, especially where trail signs, blazes and markers are absent, and a compass is of limited use without one.
In Search and Rescue, map and compass is part of our Basic Academy, and my teammates and I participate in ongoing training and practice to keep our skills, including map and compass, sharp. Not to mention to keep from getting lost ourselves while we're out looking for others.
On this page, I'll cover some of the basic elements and principles of map and compass use, but there's no way anyone can truly become proficient at one or the other or, better yet, both while sitting in front of computer or reading an orienteering book. Ongoing field practice is key, even if it's navigating right in your own back yard.
How proficient are you with a compass?
Before We Get to the Compass, Let’s Review the Map
Map Types, Their Pros and Cons
There are two basic types of maps -- planimetric and topographic.
Planimetric maps show everything in two dimensions (as a flat surface) without representing contours of the land. Spot elevations may be indicated, and the general area of a terrain feature such as a mountain or canyon may be depicted by simple labeling or a symbol, but the shape of the land is not shown. Common planimetric maps include road maps, Forest Service maps, and maps found in world atlases.
Topographic maps, on the other hand, show the detailed shape and elevation of the terrain with the use of contour lines. These maps also include much of the information found on planimetric maps, and some (like the one pictured to the right) even use shading to enhance features. The most common "topo" maps in the U.S. are the United States Geologic Survey topographic maps.
For more information on USGS Topo Maps and purchase options, visit the USGS online store.
Pros and Cons of Planimetric and Topographic Maps
- With their small scale (showing large areas), they're good for a general overview of an area for the purposes of driving or planning access;
- Show land ownership and other political or entity boundaries, such as National Forests and parks;
- Show many water sources, such as creeks, springs and stock tanks;
- They're reasonably accurate when it comes to man-made features;
- Show township, range and section locations (Learn about the Public Land Survey System);
- Handy for locating the specific topo map needed for a smaller area;
- Good for determining place names of both man-made and natural features;
- Updated more often than topo maps;
- Widely and readily available;
- Easy to interpret for people with limited map-reading skills;
- Have a simple grid system for general location, using numbers and letters around the edges of the map;
- Good for recreational information, such as camping
- Not good for getting a large-scale (close up) view of the shape of the terrain, so not good for planning hikes or other backcountry activities that require detailed terrain information;
- Don't show all roads, including many new two-tracks and logging roads;
- Not useful for vegetation information;
- Difficult to give a location by latitude and longitude, and no UTM coordinate information;
- No information on declination--the angle the magnetic compass needle is off the true (or map) north--and these maps cover a large area over which the declination would change.
Read More From Skyaboveus
- Excellent sources for terrain information;
- Good for planning hiking and other backcountry ventures requiring detailed terrain information;
- Useful for giving locations by UTM coordinates and township, range and section, as well as smaller section subdivisions;
- Good for getting a details (or large-scale) view of an area;
- Show information about vegetation and open areas by the use of color;
- Come in various scales, so you can get big (small scale) versus small (large scale) overviews;
- Include declination information for adjusting a compass ... though this information will eventually become outdated due to the change in declinations caused by changes in the Earth's magnetic field over time
- Not easy for plotting locations by latitude and longitude;
- Maps are not updated frequently, so information on roads and man-made features becomes outdated, especially in fast-growing or heavily-used areas;
- Require more advanced map-reading skills than do planimetric maps;
- More maps are needed to cover a large area
Topographic maps are the best choice for those wanting to explore the backcountry and learn to use the map in conjunction with a compass; therefore, the maps referred to hereon out will all be topographic.
Want to learn the common symbols used on topographic maps? Here's a Key to Topographic Map Symbols.
Special Orienteering Maps: A Type of Topographic Map
Special orienteering maps are even better for beginners, because they are more detailed than regular topo maps. The scale of topographic maps is generally 1:24,000, while special orienteering maps are prepared in scales of 1:5,000 to 1:20,000, showing even smaller areas.
The larger scales (smaller areas depicted) on orienteering maps make it easier to reconcile the information on the map with the actual terrain and features in the field. Symbols may vary somewhat from those used on regular topographic maps.
Map Language And Scales
The colors and shapes of symbols on a map are specific to the real objects they represent. While symbols do vary depending on which of the three different "edition types" of topo maps is being used -- provisional, new, or replacement -- the color classification is general.
The color-coding is as follows:
- Black = Man-made features
- Brown = Topographic and surface features
- Green = Vegetation
- Blue = Water-related features
- Red = Highways and land survey lines
- Purple = Features added during map revision
- White = Open areas
When using a map and compass, one must be able to determine distance on the map and then know how to convert that figure into real distance in the field. The scale of a map, shown as a ratio--the number one with a colon and then a large number to the right (ex. 1:24,0000)--is the key to making such conversions. To do so, one has to multiply the distance on the map by the divider of the scale.
"Say what?" you ask. Okay, here's an example....
If you're using a topo map in the scale of 1:24,000, one inch on the map corresponds to 24,000 inches in the field. There are 12 inches in a foot, right? So 24,000 inches divided by 12 equals 2,000, meaning 2,000 feet. Again, one inch on the map would equal 2,000 feet in the real world.
If a map uses a metric scale of 1:25,000 and a measured distance on the map is 5 cm., the real distance in the field would be 5 cm. x 25,000, which equals 125,000 cm. which is 1,250 meters.
The most common scale used for topographic maps is 1:24,000, though they are available up to 1:250,000. A 1:24,000 topo covers 7.5 minutes of latitude and longitude. Where I live, in Flagstaff, Arizona, this equals about 60 square miles, but that area changes as one moves north or south, due the "squeezing" effect of longitude moving towards the poles.
Small Scale vs. Large Scale:
This can seem somewhat counter-intutive, but if you give it some thought, it will make sense....
Small scale maps represent large areas and many square miles, with objects--both man-made and natural--appearing very tiny. For example, think about how small a house would look compared to an area that's 10,000 square miles. The small scale refers to the size of the features on the map. The larger the area depicted, the less detailed it can be.
Large scale maps, on the other hand, are more detailed, close-up views of smaller areas. A house on a large-scale map would appear bigger than on a small scale map.
See "Map Scale: Measuring Distance on a Map" for more information.
Topographic Map Contour Lines
Contour lines define the shape and elevation of the landscape. Contour lines, colored brown on a topo map, connect points of equal elevation, with each line representing one specific level. The difference in elevation between each line will be consistent on the map, and that difference--or interval--will be shown in the map's margin. The most common intervals are 20 and 40 feet.
One thing to keep in mind about contour lines is that elevation changes smaller than the designated interval will not show up on the map. In other words, if the interval (elevation difference) depicted by the contour lines is 20 feet, but a cliff is 19 feet from top to bottom, that cliff will not be visible on the map.
Every fifth contour line is called an index line. Index lines are bolder (heavier) lines, and somewhere along each index line you'll find a height above sea level expressed in numbers.
The closer together the contour lines are on the map, the steeper the terrain. Widely-spaced contour lines depict gentle slopes. Occasionally, dashed or dotted "supplementary" contour lines are drawn in level areas, with smaller intervals to show small elevation features.
The Compass: A Brief History
The compass goes back a long way--thousands of years, in fact. Its invention occurred when some smart alec (in China, so I've read) realized that lodestone -- a form of magnetite which demonstrates distinctive magnetic qualities -- when floated on a piece of wood in a bowl of water, always turned to point in the same direction.
Eventually, the compass needle -- a strip of metal magnetized by stroking it with a permanent magnet -- was developed in the 8th century (again in China), making the compass more accurate. When balanced on a pivot, the needle was able to rotate freely and, when settled, would point northward. Next, an air-filled housing was developed, which protected the needle, and this was the start of the era of hand-held compasses.
You can learn a lot more about the history of the magnetic compass on SolarNavigator.net.
Compass Parts, Terms And Functions
See the video below for a demonstration of compass parts.
Compass Parts and Terms:
Base Plate--The body of the compass, often clear plastic
Direction of Travel Arrow--Fixed in place (painted on) on the base plate, you point this arrow at the feature of interest, in the direction of travel and/or at your destination, whether using the compass ON the map or in the field.
Index Mark--This is where you read your bearing.
Mileage Scale--located on the edge/s of the compass, indicated by a ration such as 1:24,000 with marks to measure length (or distance) on the map.
Dial Azimuth Ring--also known as the Azimuth Ring or Capsule Bezel; This is the part of the compass that rotates. I'll simply refer to it as "the dial."
North/South Orienting Lines--Fixed lines on the dial, used to orient the compass to orient the compass on the map. These lines do move with the whole dial, though.
Declination Adjustment Scale--the degree lines located on one half of the inner part of the dial.
North Orienting Arrow--the red arrow that can move to adjust for declination. During field use, you'll align the magnetic needle with the arrow. This arrow, made up of two parallel lines, is often referred to as "the shed."
Magnetic Needles--the red needle that aligns with Earth's magnetic field. This needle is often referred to as "Fred."
So those are the main parts of a compass.
Now, think of the earth as a huge magnet with two poles -- magnetic North Pole and magnetic South Pole -- with invisible, magnetic lines connecting them. When the needle of a compass turns to point north after it's shaken, it's aligning with these magnetic lines of force around the earth.
There's a catch, however....
The compass needle points along those magnetic lines, but the magnetic pole is separated from the geographic North Pole by more than 1,000 miles. So one has to adjust for this difference in order to use the compass with a map.
The angle between the magnetic North Pole and the geographic North Pole from a certain place is called declination. And declination changes from place to place as well.
Be aware that certain things can interfere with the compass needle, causing deviation from magnetic north. These circumstances include the presence of steel and some local ore deposits. Even a steel wrist watch can cause such deviation, as will current-carrying, high-voltage wires.
Strong magnetic fields can permanently affect the accuracy of a compass, so be sure not to store your compass near magnets or devices that can cause magnetic fields.
A Quick Tour of the Parts of a Compass and What They're For
This is a fairly basic compass, but it's got all the basic parts you'll find on higher end models.
More About Declination
To reiterate, declination is the difference between true -- or map -- north and where the Earth's magnetic field deflects the compass needle in any particular area. In order to use compass bearings back and forth from a map (true) and the field (magnetic) and vice versa, an adjustment must be made. If this adjustment is NOT made, your compass work will likely be very inaccurate.
Be aware that a one degree error can put you off course by about 100 feet in one mile. This may not seem like much, but if you'll be traveling a long distance, try to pick a target large enough to absorb errors, such as a road, river, or power line, which you can then follow as a "handrail" to your ultimate destination.
Now, if you only take magnetic bearings in the field in order to site features and walk to them, and you aren't using a map, then you don't need to worry about declination. This is often not the case, however, and any time there's a map in the equation, declination will be an issue.
The easiest method to take declination into account is to buy a compass with a declination adjustment. Once you know the declination for the area in which you'll be hiking or working, you can set the declination on the compass and work from the map without having to think about it.
Declination is said to be either easterly or westerly, depending on which side the magnetic North Pole is from a particular area, with respect to the "line" drawn towards the geographic north pole. In the U.S., declination ranges from 30 degrees easterly in Alaska to 20 degrees westerly in Maine. The zero declination line runs from the west coast of Florida up to eastern Minnesota at the Canadian border.
To find the declination on a USGS topo map, look in the lower margin. Keep in mind, however, that declination does change over time, so note the date the map was made or last updated. An old map indicates that the declination may be out of date, so it's a good idea to find out what the current declination is. One source of this information is the National Geophysical Data Center. (Enter your zip code or Latitude/Longitude.) Here in Flagstaff, Arizona, declination changes at a rate of about 4 minutes west each year.
How To Adjust for Declination on a Compass
Brigg Abercrombie from Forestry Suppliers, Inc. shares the basic concept of declination and how to compensate for it on a compass.
Using A Compass On Its Own, Without A Map
The purpose of using a compass NOT in conjunction with a map would be to hold your course while traveling towards a distant landmark.
For example, you may be able to see your destination (or a prominent feature you know is close to or on the way towards your destination) while standing on a high ridge. But that feature may be many miles away, and once you leave your high-point, perhaps you'd lose sight of it. By taking a bearing and determining your direction of travel with your compass, you can use that bearing to continue in the right direction once you're underway.
Here are the steps...
- First, sight the feature along the direction-of-travel arrow on the base plate of your compass, keeping the compass horizontal while doing so.
- While keeping the feature object on the line, turn the compass dial until the red end of the magnetic needle -- red Fred -- is pointing in the same direction as the north/south arrow on the bottom of the capsule--the shed. Once red Fred is in that shed, your bearing is set.
- Each time you re-check your direction of travel, red Fred goes back in the shed. If you want to know your bearing in degrees, just read off the number on the dial that's lined up with the index mark.
- Now that you have your direction of travel -- a bearing -- you can begin to follow it. To do so, choose a prominent target in that direction -- it may be a distinct tree, a boulder, a post, anything you can keep track of and recognize even if you look away from it -- and walk towards it without looking at your compass. When you get to that target, get your bearing again, choose a new target, and repeat.
Remember: When Red Fred is in The Shed, you'll be facing the direction of travel.
Using a Compass With a Map: Also Known as Orienteering
Now that we've discussed maps and compasses, let's put the two together. For these exercises, I'll make the assumption that you're using a compass with a declination adjustment and that you've determined the declination in your area and already set the compass accordingly, so no calculation needs to be made.
In this next section, we'll go over:
- Orienting your map to true north
- Obtaining a travel direction from a map
- Using an intersection to determine the location of a distant feature on a map
- Using resection to determine your exact location on a map
- Using the compass as a protractor
Orienting a Map to True North
Again, this assumes you are using a compass already adjusted for declination.
To properly read a map in the field, you should first orient it, meaning that the details on the map should correspond to the landscape. And you should keep your map oriented while traveling along your route.
To orient your map, first find true north. Here's what you do:
- Set the compass bearing to north at the index mark.
- Next, lay the side edge of the compass along the map edge (or neat line). The direction of travel arrow on the base plate must point north on the map.
- Keep the compass in this position while rotating the map and compass together until the magnetic needle (Fred) is aligned with the orienting arrow (the shed). In other words, "Put red Fred in the shed." This is called "boxing the needle."
Oila! Your map is now oriented to true north. Now take a look at your map and then at what's around you and see that it makes sense.
Need more help?
This handy step-by-step slideshow with instructions onorienting your map with a compass by Backpacker Magazine is easy to follow, including making the adjustment for declination if your compass isn't already set to account for it.
Obtaining a Direction of Travel With a Compass
To reach your desired destination, follow these steps:
- First, place the compass on your map so that the long edge of the base plate connects your starting point with your destination. Of course, the base plate likely will not be long enough to actually connect these two points, but an extended line drawn along this edge should connect the two. You can use a pencil to actually draw this line on your ma