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How to Align Your Compass
Learn how to orient your map with a few basic compass skills
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Tags:
- GPS |
- Trail Tools |
- Navigation |
- Skills |
In open country and above treeline, route finding tends to be as easy as looking for the next landmark. But in forests, marshes, and low-visibility situations (like whiteouts and fog), you'll need a compass to orient your map. A few basic skills simplify the art of compass navigation.
- Determine the magnetic declination for your area (see "Declination 101" below), and set your compass for that variance, which is marked on most maps.
- Orient the map so its grid lines point toward true north. This orients map to landscape, so you can correlate contour lines with surrounding features.
- Place the compass on the map so the baseplate's long edge (and direction arrow) point from your map position to your intended map destination.
- Hold the baseplate in alignment with your intended route, and rotate the compass bezel until its markings align with the magnetic needle. Now the north-south arrow on the rotating bezel points to magnetic north, while the baseplate arrow points along your intended travel vector, called a heading.
- When obstacles deflect you off course, note the compass bearing of the direction you walk or paddle (say you have to detour around a giant boulder at 45 degrees), then count your steps, strokes, or the time you spend off-course. After skirting the obstacle, return to your original course for the same steps, strokes, or time. (In this case, it's 315 degrees; 360 degrees - 45 degrees = 315 degrees.) Then resume your primary heading.
Follow The Leapfrog
In heavy fog or featureless terrain, use your hiking or paddling partners as intermediate objects. Send them forward as far as possible and wave them into position along your course. Then leapfrog ahead. Give them the compass as you pass so they can repeat the leapfrog.
Rock To Rock
In low-visibility situations, take note of any obvious landmark in your line of travel, then move single-mindedly until you reach it. When you get there, take another sighting, pick a new intermediate objective, and repeat.
The Two-Mile-An-Hour Speed Trap
An oft-stated rule of thumb for walking speed is 2 miles per hour. But that's for a dayhiker on an easy trail. It doesn't account for heavier loads, gazing time, rest stops, photos, or lunch breaks. Plan to average about 1.5 miles per hour if you move steadily on a good trail. Heavy loads, rough terrain, rest stops, or water searches slow you down further.
COMPASS TIP: Declination 101
Maps are oriented toward geographic, or "true," north (the North Pole), but compass needles point to magnetic north, a place that wanders slowly within the Canadian Arctic. The difference in angle is called magnetic declination, and it varies from 21 degrees west in Maine to 26 degrees east in Alaska. That's why you should buy a compass with adjustable declination and set it properly.
On most compasses, adjusting declination is done by turning a tiny metal screw on the rotating compass needle housing. Look for declination on the lower left portion of your topo map; you'll see two diverging lines with the angle listed between them. If it says "16 degrees east," rotate the compass housing so the magnetic north/compass needle mark sits 16 degrees to the right (east) of the true north orienting lines. Twist the screw to reach the proper orientation.
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READERS COMMENTS
Some very simple, easy to follow, illustrated compass instructions for adults and kids are in a childrens hiking book on Amazon titled: Felix the Sugarglider Be Safe Hike Smart. We read this book before every hike to refresh our knowledge on safety, packing, and direction/orientation skills.
Posted: Oct 15, 2011 AZ Hiker
Edit update: Bullet point number 5 under How to Align A Compass has been rewritten for clarification.
Posted: Feb 05, 2010 Kris Wagner @ Backpacker
One of the better ways to "defeat" declination problems is to draw magnetic north lines on the map at one inch intervals. Do not, repeat, DO NOT, try to use the diagram arrow at the lower left of the map. It isn't long enough to give a reliable set and printing techniques aren't refined enough to give you an accurate set.
Use a ten or twelve inch diameter circular protractor and take your angular declination measurement from the lower left corner of the map. The bottom margin line and left edge line should be at 90 degrees to each other. You cannot count on that with the other three corners.
A one degree error in these lines can give you catastrophic errors over long distances. 1 inch equals 1 minute of angle at one hundred yards, ergo 1 degree equals 5 feet at one hundred yards and 88 feet at 1 mile. A one degree error on a bearing taken on a topo feature at 5 miles will give you a quarter mile error at the hikers end of the bearing. Consider that most compasses are calibrated in 2 degree increments.
Make sure your magnetic north lines are reasonably precise. Errors there will compound compass reading errors in the field.
Al Limberg
Concord, CA
Posted: May 22, 2009 Albert Limberg
I believe a simpler way to determine a direction is to orient the map to the north by laying the compass along the magnetic line shown in the declination diagram. Then lay the compass between your starting point and destination, rotate the bezel ring to north and that will give you your direction of travel. There is no need to set the decliantion then orient the map to true north.
When skirting obstacles, if you follow a back bearing as you suggested you will end up where you started. If I travel right 50 paces, after clearing the obstacles I will travel left 50 paces. It is also a good idea to alternate the direction you go to avoid the obstacle. 1st obstacle go right, 2nd obstacle go left, and so on. People tend to drift to there dominant side if they always take the same direction around an obstacle.
Posted: Sep 12, 2008 Ken LaFlamme
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