How to Use a Compass With a Map, Step by Step, Declination Included

The plateau is perfectly clear at the start. Then fog climbs out of the valley, the cairn across the way disappears, and the faint trail fades into the short grass. That’s when the compass stops being a gadget at the bottom of your backpack and becomes the most useful thing you carry, as long as you learned to use it before you needed it.

Ordnance Survey, Britain’s national mapping agency, puts it plainly: phones and mapping apps are hugely useful, but batteries die and signal drops, while a compass works anywhere [1]. It doesn’t replace the map, it completes it: the map tells you where to go, the compass tells you which way.

A hiking compass, part by part

The baseplate compass hikers use comes down to five parts [1]. The clear baseplate, whose straight edge works as a ruler between two points. The magnetized needle, whose red end points to magnetic north. The rotating dial, or bezel, marked from 0 to 360°. The orienting lines and arrow at the bottom of the housing, which you line up with map north. And the direction-of-travel arrow on the baseplate, which shows the way to go.

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A bearinga direction measured clockwise from north, from 0 to 360°: 90° is east, 180° south, 270° west is simply a precise direction. You don’t need to memorize the numbers to start: what matters is that the dial holds the direction once it’s set [1].

Taking a bearing from the map, in four moves

1. Line up the two points. Lay the compass flat on the map with one edge of the baseplate running from where you are to where you’re going, the direction-of-travel arrow pointing toward your destination.
2. Turn the dial to map north. Without moving the baseplate, turn the dial until its orienting lines run parallel to the map’s north-south lines, orienting arrow toward the top of the map. The bearing is set; ignore the needle for now.
3. Line up the needle. Lift the compass, hold it flat in front of you, and turn your whole body until the red end of the needle sits inside the orienting arrow.
4. Follow the direction-of-travel arrow. Pick a fixed landmark far ahead along its line, a lone tree, a boulder, a summit, hike to it, then repeat.

These four moves are the ones Ordnance Survey teaches beginners, summed up in a phrase British hikers love: put “red in the shed,” the needle inside its arrow [1]. It also flags the two most common mistakes: moving the dial once it’s set, and not holding the compass straight out in front of you [1]. Aiming for a landmark rather than hiking with your eyes glued to the needle also gives you a truer line [1].

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The needle’s north isn’t the map’s north

There are three norths, and this is where beginners get tangled up [2]. True norththe direction of the North Pole, around which the Earth spins, the north of the meridians. Map or grid north, the north of the map’s grid lines. And magnetic north, the one the needle points to, which shifts slowly from year to year [2] [3]. The angle between true north and magnetic north is called magnetic declinationthe angle between true north and the north shown by a compass, measured east or west; it varies with place and date [3].

We calculated it for October 23, 2026, with the World Magnetic Model, WMM2025, run by NOAA and the British Geological Survey [4] [5]. In the US, it’s anything but small: 14.6° east at Mount Rainier in Washington, 12.3° east in Yosemite Valley, and 15.3° west at Mount Katahdin in Maine [5]. France’s national mapping agency, by contrast, describes it as “almost zero in mainland France today” [3]: our figures show 0.05° in Brest, but 3.2° east in Chamonix and 3.5° east in Strasbourg [5].

Do you need to correct for it? On a trail with landmarks everywhere, 2 or 3° changes nothing. Off trail, on featureless ground, or in fog, it matters: France’s mapping agency notes that a 1° error on a point about 4 miles (6 km) away puts you roughly 330 feet (100 m) out [3], and at 15° the error grows fast. The rule is simple: when magnetic north is east of map north, subtract the declination from a bearing taken off the map before following it; when it’s west, add it. The legend of a map gives the value at its edition date, and the NOAA and British Geological Survey calculators give it to the day [4] [5].

Hiking in France? Since March 2014, the edge of the paper on IGN maps, the French equivalent of USGS topos, follows the map projection rather than true north, a difference that reaches 5.5° near Brest [3]. For a precise sighting, IGN advises lining up with the meridians, or calculating a declination relative to the map edge, and keeps those calculations for uses beyond everyday hiking [3]. Older IGN maps printed before March 2014 had edges aligned with true north [3].

Practice before you need it

A compass is best learned in good weather, on ground you know: that’s Ordnance Survey’s advice, and I can’t think of better [1]. A familiar loop, a bearing at every junction, and the moves become second nature before the day they count. To go further, an orienteering club or a guided navigation course teaches you to read terrain and pick landmarks far better than any article. On marked trails, the compass mostly confirms the blazes, which our guide to trail markers and blazes helps you read; and to know how long the way back will take, estimate your hiking time.

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Worth watching

REI walks through the parts of a compass, setting declination and taking a bearing from a map and in the field, the three steps this guide covers.

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Guillaume Hoarau

Camping, backpacking, bushcraft and hiking

Guillaume Hoarau writes for Outfarer about camping, backpacking, bushcraft, and hiking. A survival-skills buff and a collector of vintage field manuals, he loves clear explanations, lists that actually help and other people’s stories, which he tells well.

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