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Map & Compass: Adjust for declination & orient the map

Backcountry navigation is an art. The basics can be learned quickly, like dead reckoning, reading a map, and using an altimeter watch. But extensive practice is necessary to seamlessly and flawlessly apply these skills in the field, especially when under duress or in challenging situations, like off-trail in a heavily forested area with rolling hills.

In the first two instructional videos, I focused on a single aspect of navigation: how to use a compass.

Magnetic declination

Watch the video, starting at 0:16

Before you start spinning the bezel and baseplate, you must understand magnetic declination. Or, really, you just need to know its effect: that the magnetic needle on your compass does not point at True North, i.e., the geographic North Pole, or where Santa Claus lives. Instead, it aligns with the Earth’s magnetic field, in a direction known as Magnetic North.

A topographic map will specify the angular difference of True North and Magnetic North. In the US, the difference is essentially zero when near the Mississippi River — Minneapolis, St. Louis, New Orleans, etc. In this zone, the magnetic needle still aligns with the Earth’s magnetic field, but simultaneously it points at True North, too. When east of the Mississippi (e.g., Boston), the needle pulls west to the river, and True North is to the east. When west of the Mississippi (e.g., Denver), the needle pulls east towards the river, and True North is to the west.

Don’t get this wrong, or your bearings will be incorrect by twice the declination. If you live in Seattle, where declination is 15 degrees East, that would be a 30-degree error!

Adjust for declination

Watch the video, starting at 2:50

An inexpensive baseplate compass like the Silva Start 1-2-3 will be non-adjustable. When finding or transferring bearings, you must manually account for the declination.

For regular compass use, I recommend an adjustable compass; the Suunto M-3 D Leader is a good option, but I like the Suunto M-3 Global because of its more forgiving needle. With an adjustable compass, the orienting arrow (“the shed”) can be rotated relative to the bezel by twisting a small screw on the back of the compass.

Observe the difference below. Both compasses are pointing north. I live in Boulder, Colorado, where the declination is 8 degrees East.

A non-adjustable (left) and adjustable compass (right), both pointing towards True North. With the non-adjustable compass, the needle is positioned to the right/east of the orienting arrow ("the shed"), whereas with the adjustable compass the needle is positioned directly over it.

A non-adjustable (left) and adjustable compass (right), both pointing towards True North. With the non-adjustable compass, the needle is positioned to the right/east of the orienting arrow (“the shed”), whereas with the adjustable compass the needle is positioned directly over it.

Orient the map

Watch the video, starting at 3:40

By orienting the map, you align the spatial features on the map with those in the field. In general, it makes much clearer where you have come from and where you need to go. For example, suppose you reach a trail junction where the signage has fallen over. Assuming you know where you are on the map, you can orient the map and identify which trail is which.

To orient the map, first:

  • Line up the edge of the compass with the edge of the map, or
  • Line up the meridian lines (the parallel lines inside the bezel) with a north/south grid line on the map

This latter option is a cheat since grid lines have their own declination value. (They are oriented to Grid North, which is not necessarily the same as True North or Magnetic North). But the value so small as to be functionally irrelevant, at least for backpacking.

Your compass bezel need not be rotated to zero degrees (True North), but conceptually it may help.

Next, rotate your entire body until “red is in the shed.” (Or, if you are using a non-adjustable compass, until the needle is at the correct declination.)

An oriented map, done in a few different ways. Normally I rotate the bezel to TN/0 degrees, then line up the edge of my compass (or the meridian lines inside the bezel) with the edge of the map. As a cheat, you can use grid lines on the map, but this will be slightly less accurate.

An oriented map, done in a few different ways. Normally I rotate the bezel to TN/0 degrees, then line up the edge of my compass (or the meridian lines inside the bezel) with the edge of the map. As a cheat, you can use grid lines on the map, but this will be slightly less accurate.


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13 Responses to Map & Compass: Adjust for declination & orient the map

  1. scotty July 16, 2016 at 11:15 pm #

    Any chance that backpack in the intro is the one you’ve been working on? When might we get the details?

    • Andrew Skurka July 17, 2016 at 6:14 am #

      Yep, that’s it. The one in the videos is a prototype, and a few tweaks will be made before production. It’s a Spring 2017 product. Here’s the press release about it:

      The Sierra Designs Flex Capacitor 40-60 backpack features a unique gusset system that allows the circumference to quickly expand from 40 to 60 liters with the adjustment of a few straps, providing a more stable and comfortable load carry. This multi-day pack features a unique “Y-FLEX” suspension that’s designed to be as lightweight as possible, allowing redundant materials to be removed without sacrificing comfort or stability. The pre-bent vertical stay transfers the pack weight into the waist belt, while providing space from the back for maximum ventilation. Other features include EVA foam padding, stretch mesh side pockets and a removable hydration sleeve. The Flex Capacitor will be available in 2 torso sizes: small/medium (17”-19″) and medium/large (19”-21″). MSRP: $189.95

  2. Sheila July 24, 2016 at 3:38 pm #

    Nice timing, Andrew! I am just about to brush up on my navigation skills for a big walk I’m planning, so this is very timely and a nice addition to the reading up I’ll be doing. Your website is really excellent for all the information it offers and I will be using several of your recipes during the walk, although I’ll have to adapt some slightly for the ingredients I can find in Australia. Looking forward to the next videos.

  3. Dhaval August 7, 2016 at 2:14 pm #

    When is second part coming in this navigation skills series? eagerly waiting….

    • Andrew Skurka August 7, 2016 at 7:27 pm #

      Tomorrow, I believe. The SD team was at a big tradeshow last week and the office was pretty quiet.

  4. Kevin March 19, 2018 at 8:15 pm #

    When you orient the map with a nonadjustable compass does the magnetic needle need to be in the shed after adjusting the declination? And then will the map be aligned ? Thank you!

    • Andrew Skurka March 21, 2018 at 4:50 pm #

      When you orient the map with a nonadjustable compass, the needle should be to left/west or right/east of the shed in accordance with the declination for the area. For example, in Boulder, Colo. (where declination is 8 degrees), I would line up the edge of my compass with a known north-south line on my map, and then rotate my entire body until the needle is 8 degrees to the right/east of the shed.

  5. Mike July 10, 2018 at 11:27 pm #

    1) So orienting the map you want to factor in the declination into that orientation?

    2) with the map now oriented with declination factored in, can I just take a 220 azimuth from the map and set the compass to 220 and follow that?

    3)if I take a reading with my compass of say 300 can I plot 300 on the map since the map is oriented with declination?

    • Andrew Skurka July 11, 2018 at 12:13 pm #

      1. When you orient the map, yes, you need to account for the declination. Align the orienting lines (which are inside the bezel) with the map’s north-south margin or grid lines, then rotate the map and compass together until “red is in the shed” (assuming you have an adjustable compass; if not, the needle needs to be east or west of the orientating arrow per your location’s declination.

      2. The map does not need to be oriented before finding bearings on the map. You could find bearings on the map while holding the map upside down or vertically — the relative positions of objects on the map do not change.

      3. If you find a bear in the field of 300-degrees, you can apply that back to the map, regardless of whether the map has been oriented. Same reasoning as explained in #2.

      I think you need to read and watch Part 2 of this video series, https://andrewskurka.com/2016/map-and-compass-find-transfer-bearings-map-field-video/. It answers your questions.

  6. Mike July 10, 2018 at 11:31 pm #

    I have a Silva compass that is older and the 380 degrees on the bezel go in counterclockwise direction beginning with zero. Why is this? I always thought degrees go clockwise?

    • Andrew Skurka July 11, 2018 at 12:07 pm #

      Hmm, never heard of a compass like that. Try contacting Silva directly.

      • Mike July 16, 2018 at 10:43 am #

        Hi! I did some more research and apparently there are two types of compasses. This is from Wikipedia.

        “The direct reading compass has graduations on the housing which read anti-clockwise round the face, with zero on the far side. The effect of this configuration is that if the housing is aligned with a direction, the north point of the card or needle will point directly towards the number representing the bearing. No further effort is needed on the part of the operator, you just find the number the arrow points at and read off the bearing. The bezel has no graduations, it is just a marker to align the card.[5]

        The indirect reading compass has graduations on the bezel. These graduations are clockwise round the face, and the zero mark coincides with the notch. To take a bearing the compass must first be aligned with the direction, then the bezel must be turned so that the notch aligns with the north point of the card or needle, and the bearing can then be read at the far side of the compass.[5]

  7. Dan Weinstein July 15, 2018 at 5:51 pm #

    This video compliments this article nicely https://youtu.be/9A2vl0EK_2U

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