GPS and Compass: 3 Reasons Why You Need Both in the Backcountry
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.
Lensatic Compass or Baseplate Compass: Which One is Right for You?
Serious outdoor enthusiasts are divided on the question of whether to pack a lensatic or baseplate compass. Here’s a quick rundown of the differences between these two types of compasses in terms of ease of use, precision, and packability to help you take sides.
The Difference Between a Lensatic and Baseplate Compass
A baseplate, or protractor compass, has a clear, plastic base that can be used as a protractor on a topographic map, and a magnetic needle that swings in a capsule filled with fluid to dampen quick movements of the needle. The most accurate models have a folding mirror that allows the user to read the compass (reflected in the mirror) while sighting distant objects.
A lensatic compass uses a lens to allow the user to read the compass bearing with just a quick downward glance while sighting. These compasses generally use a magnetic disk rather than a needle, and dampening with either fluid or, in the best models, electromagnetic induction.
Ease of Use
Both types of compass require a little study and practice, and neither have a clear advantage in ease of use. The lensatic compass may have a slight advantage in initial comprehension for beginners because the direction seen through the lens is always the way you are facing. With a baseplate compass, the dial (bezel) has to be set before the bearing can be read. A disadvantage of the lensatic is the lack of a magnetic declination adjustment—this correction has to be done mentally, which is not a big deal, but introduces an additional opportunity to make a mistake.
Compass Precision
Used properly, both types of compass can produce reasonably precise readings, but the lensatic compass has a slight edge. The narrow, magnified field of view seen through the lens, with just a glance down to read the direction, is a powerful combination. However, for most outdoor recreational activities like backpacking and hunting, a degree or so extra precision probably isn’t going to be the deciding factor.
Packability
Weight and bulk are factors to consider, especially if you do long-distance backpacking, lightweight expeditions, or any other activity where every ounce makes a difference. High-quality mirrored baseplate compasses weigh less than 3 ounces and have a slim profile of just over a half inch. The rugged, aluminum Cammenga Model 27 is twice the thickness and twice the weight, but it is very durable, and has no liquid, so leaks are not an issue.
How to Make a Compass
Making a compass to demonstrate the concept of magnetism is easy. Simply magnetize the point of a sewing needle by rubbing it on a magnet–try to do this in just one direction. Then float the needle in a bowl of water. If the surface tension of the water is not sufficient to keep the needle afloat, use a small piece of cork to float the needle.
Compass Bubble
A small bubble appearing in a fluid-filled handheld compass is generally not a problem. It develops due to changes in temperature and atmospheric pressure, usually getting larger with increasing elevation and decreasing temperature. I live at 7,000 feet elevation and I own several compasses. They all have bubbles here, but when I descend to lower elevations the bubbles disappear.
Manufacturers of handheld compasses, including the popular Silva brand, recommend replacing the compass or having the fluid-filled capsule replaced if a bubble ¼ inch in diameter or larger develops. These large bubbles are indicative of a slow, invisible fluid leak.
Keep in mind that the purpose of the fluid is to create dampening effect. The compass would still work even if no fluid was present as long as the bearing is good enough to allow the needle remained free to swing without scraping the top or the bottom of the compass housing. I lost all the fluid from a Silva Ranger CL and discovered that it definitely does NOT work with out fluid. The needle just jerks around and stalls even if it is not touching the housing.
A large bubble that still covers the pivot point of the needle usually just affects the speed at which the needle comes to a rest, but there may be some tension effects that could slightly affect accuracy even if the needle is not scraping the housing. Replacing or repairing a compass with a large bubble is a must because it means there is a leak and eventually you will lose all the fluid and the compass will become useless.
Small bubbles in mounted compasses, including marine compasses are potentially more problematic than those in a baseplate compass—mostly because the stakes are often higher. Hiking a few miles out of your way is usually not as serious as boating off course.
A few compass designs incorporate the presence of a bubble to help the user keep the compass level, but this is very uncommon. Most mounted compasses should not have a bubble. Here is an excerpt from the Richie Navigation FAQ for their popular marine compasses:
“Ritchie compasses are designed to not have a bubble; if you see a bubble, there is a leak. This may seem unlikely to you, because you may not have noticed any fluid escaping from the compass. Ritchie compasses are filled with Isopar L® or odorless mineral spirits. Both tend to evaporate before it is noticeable. Bubbles may cause a number of problems, so it is recommended that you have the compass repaired as soon as possible.”
Diving compasses are another type of compass that warrant a little extra attention if a bubble develops. Like with a handheld, baseplate compass, the primary concern is uneven pressure or surface tension causing the needle—or the card in this case—to touch the housing and not swing freely. So, a small bubble is not a big deal, but then again, a compass is among the least expensive items in you diving gear, so consider replacing it to be on the safe side. If you do, keep your old one to test beside the new one—it will enhance your experience and may help you provide some good advice to a dive buddy someday.
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