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Backpacker Magazine – May 2010

Navigation: Exploring Off-Trail

When your route takes you off-trail you can still be on course with these navigation tips.

by: Kristin Bjornsen, Dougald Macdonald, & Kristin Hostetter


Find True North
Unfortunately, magnetic north (where the compass points) is not true north (the North Pole). The difference between the two (called magnetic declination) varies with location and is listed in the map key. Since most maps are oriented toward true north, you must correct your compass bearings to get an accurate direction. To do this, adjust the orienting arrow on your compass to whatever the declination is (for instance, about 14 degrees east in central Colorado). If your orienting arrow isn’t adjustable, make the correction by subtracting east declinations and adding west declinations to true bearings (“East is least; west is best”). For example, if your central Colorado map shows a 90-degree bearing (the true bearing) to reach a hilltop, you’d set your compass to 76 degrees (the magnetic bearing).










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READERS COMMENTS

Star Star Star Star Star
Jeff Treiber
Apr 13, 2014

Great series of articles. I wish they were available as one .pdf instead of a bunch of separate web pages. Keep up the great work; this is the best "outdoors magazine" there is!

Star Star Star
greg
Jan 04, 2014

In article's Section 1 (Take Bearings from a Map), second paragraph needs to reference A, B, C labels in illustration to make good sense. Or probably a second illustration with labels. Also second paragraph switches to or adds new terminology not used in first paragraph. If this is for novices it cannot assume understanding beyond square one.

Lyn G
May 14, 2011

You DO NOT need to account for declination if you're simply taking a bearing from a map. You need to align either the left or right edge of the map to magnetic (not true) north, and then hold the map in that position and take all the bearings you need.

However, if you try to triangulate, you WILL need to consider declination. For that reason, it is far easier to draw declination lines on your map and take all bearings from those lines. Then you do not need to orient the map towards magnetic north. All you need to do is line up the meridian lines inside the bezel to the declination lines and rotate the direction of travel to your starting/ending points.

Lyn G
May 14, 2011

You don't need to worry about declination if you're taking a bearing from a map and you orient the compass and map to magnetic north. However, if you try to triangulate, you will need to include declination, so it is a good practice to draw the declination lines on the map and always orient with those lines. Also, the only true north-south lines on a map are the right and left edges, a lot of lines on the map are section and township lines which are not necessarily true north-south.

JRS
Nov 12, 2010

You do need to account for local declination whenever you use a map and compass together. The map is aligned to true north, but the compass needle, unless adjusted for declination, is responding to magnetic north. Learn how to orient your map with a compass here: http://www.backpacker.com/backpacking_101_how_to_align_your_compass/skills/12156

Geargeek
Sep 24, 2010

Correct me if I am wrong, but do you not have to accout for the declination of Magnetic North when you go from map to compass?

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