It is easiest to answer this question with a picture. Check out the map below from the National Geophysical Data Center. Declination is the same at any point along one of the lines (called isogonic lines). Notice the vertical blue line with a 5 on it in the middle of the map. This is the 5 degree east magnetic declination line. If you walked from North Dakota all the way to Mexico you would be following the same path as this line and you could leave the magnetic declination on your compass set to 5 degrees east.
On the other hand, if you were to walk from Boston to San Francisco there is a 30 degree difference in magnetic declination (from about 15 degrees west at Boston to about 15 degrees east in San Francisco). So, you would have to adjust your declination frequently as you crossed the country if you wanted to be able to use a map and compass together.
More information on magnetic declination maps can be found at the NOAA NGDC site.
If your compass does not have a magnetic declination adjustment, you may need to add or subtract degrees from your direction of travel to compensate for the difference between true north and magnetic north in your area of travel. I say may, because if you are using a compass to navigate to and from a destination without a map, there is no pressing need to account for the difference between true north (which your map is oriented to) and magnetic north. The exception is when you are also using sun angles and other techniques to determine direction and you are in an area with a huge difference between magnetic and true north. Here, making a correction would help you switch back and forth between compass and sun/celestial navigation.
If you are using a map (which you should be) you will first need to determine the magnetic declination for your area (see Finding Declination for Your Area). If it is an east declination you will subtract the appropriate number of degrees when taking bearings from a map (east is least) and add degrees when you sight an object with your compass and want to transfer that bearing to the map.
For example, If you are going for a cross-country hike near Portland, Oregon where you have an approximate magnetic declination of 20 degrees east (this means your compass is pointing toward the magnetic north pole which is 20 degrees east of north on the map). Let’s say you place your compass on the map, lining up the edge of the compass with your starting point and your destination (or landmark of interest). To determine your bearing, you twist the dial until the orienting lines on the bottom of the compass line up with north on the map, then read the compass direction. Let’s say this direction, which is true north, is 85 degrees. You will now need to twist the dial to set your compass to 65 degrees before using your compass to navigate toward that destination.
Let’s do another example. If you are hiking in upstate New York, the magnetic declination is closer to 15 degrees west. If you were to plot a course of 50 degrees on a map, you would add 15 degrees and set your compass to 65 degrees for navigation.
There are several mnemonic phrases and rhymes to help you remember how to make these corrections. I created my own to reflect my forestry profession:
“Every Day Tree Tops Make Shadows”
The translation is, “East Declination True to Magnetic Subtract.” In other words, if I am in an east declination area and plotting a course on a map (true north) and need to correct it to magnetic north (compass) I subtract the appropriate number of degrees when I set the compass. Conversely, I add degrees if I am converting between a compass bearing (magnetic) and map bearing (true) in this same east declination setting. Adding and subtracting is reversed in a west declination area.
GPS and Land Navigation is an instructional video on how to use a GPS, compass, and map for navigating on foot. The information provided is accurate, and thorough, but because of the breadth of topics covered, it is a little shy on details in places. It’s also a little heavy on some less than informative scenes of people walking through the desert staring at gps screens. That said, it is the best DVD currently on the market that covers land navigation–until, that is, Roadside Nature releases it’s next DVD covering advanced map, compass, and GPS (in the interest of full disclosure, Compass-Howto.com staff are involved with the production of the Raodside Nature DVD series).
This 50 minute DVD covers the basic skills needed to use a compass by itself, or with a map to navigate on land. The narrator is a former park ranger and forester who has taught map, compass, and GPS techniques at one of America’s top forestry schools for over a decade.
The information is presented in a clear, concise format and includes several examples and a review at the end of each section. The lessons are geared toward beginning and intermediate compass users.
Topics covered in the DVD:
• What magnetic declination is and how to set a compass for the declination in your area.
• How to use a map and compass to confidently hike cross-country where there are no roads, signs, or trails.
• How to use the Public Land Survey System (Township and Range) to pinpoint your location practically anywhere in the western U.S.
• Which compasses are best for outdoor recreation like hiking, hunting, bird watching, backpacking, and camping.
• How to set, sight, and read a compass.
• How to plot directions on a map with a compass.
• Why a global positioning system complements map and compass skills but does not replace them.
Now several editions beyond its introduction in 1955, Be Expert With Map and Compass is still an excellent reference book for learning map and compass skills. Some of the photos and illustrations are a little dated, but the information has been kept current.
Bjorn Kjellstrom was one of the inventors of the Sylva orienteering (or baseplate) compass, and was instrumental in the foundation of the sport of Orienteering. A third of this 220 page book is dedicated to the sport, which has been steadily growing over the past few decades. There is also a section on wilderness navigation, but the bulk of the book focuses on learning how to use a compass.
Beginners and intermediate compass users will benefit most from Be Expert With Map and Compass, and if you are thinking of getting involved in orienteering, this book is the authority on the sport, as the subtitle, The Complete Orienteering Handbook, suggests.
A Review of Wilderness Navigation: finding your way using map, compass, altimeter, and GPS. second edition by Bob Burns and Mike Burns
Wilderness Navigation packs an encyclopedia worth of outdoor navigation skills into a 150 page book. Accomplished mountaineers and outdoor skills instructors, Bob Burns and Mike Burns, achieve this by boiling their content down to include only those skills and techniques that their decades of experience have shown to work.
They devote very little space to techniques like drawing magnetic north lines on topographic maps and doing the manual calculations to correct for magnetic declination. Instead, they write what I would have—buy a compass with a declination setting because a cold, dark wilderness situation is the last place you should be doing math (but learn the “manual” technique just in case you get into one of those Apollo 13 situations).
Wilderness Navigation is aimed at mountaineers and hard core wilderness enthusiasts, but it is very clearly written and, I think, well-suited to “advanced” beginners. If you have an analytical mind and tend to easily understand new techniques and technologies, you should easily be able to start from scratch and learn everything you need to know for map and compass and GPS navigation from this book.
There are even 30 practice problems in the Appendix to test your knowledge, and practicing these navigation techniques before embarking on your mega-transect across the Congo Basin is essential. But Wilderness Navigation, and a little practice, is all the average backpacker, hunter, hiker, or birder will ever need to become a competent and confident outdoor navigator.
Staying Found is a small, 150 page book, now on its third edition. It includes a good section on how to use a compass as wells as chapters on using maps, route planning, and teaching kids how to not get lost. The compass section has some good practice tips and exercises for beginners.
Fleming’s presentation is clear and concise, and is clearly aimed at the beginner. I would recommend this book for younger outdoor enthusiasts who are concerned about getting lost in the wilderness and looking for an introduction to the subject. It is also an affordable reference guide for occasional backpackers who would like to refresh their knowledge before a trip.
First published a year after Harold Gatty’s death in 1958, this book was originally titled Nature is your guide. It summarizes a lifetime of observation and research by a professional aviator and navigator who, in 1931 set a record by flying around the world in 8 days. During World War II, Gatty played a vital role in air navigation research, and all the while, he was clearly fascinated with how people found their way around before the invention modern navigational instruments.
In his book, Gatty explains the mysteries of how “primitive” humans managed to achieve almost supernatural feats like colonizing the islands of the Pacific Ocean or traveling between remote villages with nothing but ice and snow as landmarks. He reveals the abundant natural signs that our modern lifestyle has dimmed our ability to see. To our ancestors the clues would have been as easily readable as road maps or traffic signs are to us.
Finding Your Way Without Map or Compass helps us relearn some of these forgotten navigation signs. Gatty shares examples of indigenous knowledge and his own observations for using sun angle, the night sky, wind direction, plant forms and diversity, and even wildlife behavior as navigational guides.
For example, data on the distribution of sea birds at locations throughout the Atlantic Ocean can be used to indicate the direction and distance to land. The shape of sand and snow dunes can be used to indicate direction. One of my favorites is the analysis of cloud patterns and reflections in the sky that indicate the presence of mountains or water bodies beyond the horizon.
Some of the topics in this book are a little broad for the average hiker trying to hone her skills in backcountry travel, but most sections have at least some application for modern outdoor enthusiasts. The thorough treatment of how sun angle, in combination with latitude and wind patterns, causes different tree characteristics is especially useful for wilderness hunters and backpackers.
If you have ever wondered if moss grows on the north side of a tree or if the hands of a watch can be aligned with the sun to work like a compass, you should read this book.
It is a popular misconception that the handheld GPS (and other “location aware” devices like the iPhone) completely replace a map and compass for land navigation. In some cases, like an afternoon hike on a well-traveled hiking trail going sans map and compass is probably fine, but for serious outdoor adventures, a compass (and a map) is an essential companion to your handheld GPS. Here’s why.
1. Determining Directions with GPS Only Works while Moving
GPS units display accurate directions to you only while you are moving. When standing still or moving very slowly you’ll get directional readings that vary wildly, which is not very handy if you are standing on top of a mountain trying to figure out which direction you are facing.
Some handheld GPS units and newer iPhone models have built-in electronic compasses that work independently of GPS satellite communications through a technique called magnetic induction. These electronic compasses detect the Earth’s magnetic field, producing the same result you would get with an “analog” compass. Accuracy of sophisticated electronic compasses for marine navigation can be very high (to match the 4-digit price tags), but don’t expect more than 2 to 5 degrees of accuracy with your handheld GPS or mobile device compass.
2. Distant Terrain Features are Easier to Work With when Using Map and Compass
Trying to figure out your location on a small GPS or iPhone screen can be challenging in a backcountry environment (especially if you lose satellite coverage!). Plotting courses on a paper map not only works without satellites, but allows you to view topography information over a broad area without zooming in and out. Another reason to bring along a compass is that it is difficult to accurately plot bearings on a map with a gps or phone.
3. No Batteries Needed
Finally, the possibility of a malfunction is much smaller with a handheld compass. Rugged gps units rarely just stop working, but it does happen—especially when they get dropped on hard surfaces. They also go through batteries very quickly if you are referring to them constantly. A better solution is to use your GPS power sparingly and refer to your battery-free compass often.
Silva, Suunto, or Brunton?
All three of these companies make good handheld compasses for land navigation and all three also make some low end compasses that I would not recommend. At the top end, it is difficult to say which company builds the compass that will perform the best or last the longest, so I would focus on the getting your favorite features for the best price rather than reputation because just who is making the compass that you are inspecting is not as straightforward as you might expect.
In 1932 Silva became the first manufacturer of the baseplate (orienteering) compass, and built a reputation for quality around its Silva Ranger and other models. However, in 1985 , Johnson Worldwide Associates (now Johnson Outdoors Inc.) bought the North American side of the Silva company, and beginning in the late 1990s, compasses like the Ranger are no longer manufactured by Silva. Over the past few years I have seen an increasing number of negative reviews of the Silva Ranger, so there is some question about quality control since the transition to Johnson Outdoors. However, there is also an indication that the Suunto company manufactures compasses for Johnson Outdoors, so I am not sure I believe in any huge discrepancy between the quality of these two brands. I have used both for many years.
The original parent company of the Silva Ranger is now called Silva Sweden AB and it still sells compasses under the Silva name outside the U.S., but get this, it has owned Brunton since 1996. So the Brunton Model 15 sold in the U.S. could be considered a more direct descendant of the Silva Ranger than the Silva Ranger that Johnson Outdoors produces. To make matters more confusing, some of the original Brunton-designed compasses are sold under the Silva brand name outside the U.S.
Suunto brand compasses were not involved in the acquisitions and legal dealings that produced today’s complicated brand identification, but the company apparently manufactures some compasses for Johnson Outdoors to be sold under the Silva name in North America.