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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


Decipher the map key
>> Scale Tells you the ratio between a distance on the map and the actual distance. A 1:24,000 scale means that one map-inch equals 24,000 ground-inches, or about one-third of a mile. Most maps also have a graphical bar showing the scale (e.g., 2.5 inches equals one mile).
>> Contour interval The elevation change between each contour line
>> Symbols The markings used to denote trails, streams, mines, etc.
>> Date of publication and revision Reveals how current the map is
>> Magnetic declination The difference in degrees between true north and magnetic north. Since the latter drifts with time, for old maps, get the latest declination at ngdc.noaa.gov/geomagmodels.
>> UTM zone number UTM refers to the Universal Transverse Mercator coordinate system, a grid that’s similar to latitude/longitude but based on the metric system. The zone number indicates which of the UTM’s 60 zones you’re in—vital info for taking waypoints from a map.

Find North with Polaris
Locate the two stars at the rim of the Big Dipper’s cup (called the pointer stars). Draw an imaginary line between them, and follow it (about five times the relative length) to Polaris, the North Star, which is the tail-end star of the Little Dipper. The North Star typically lies within one degree east or west of true north. This only works in the northern hemisphere.


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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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