How to navigate with a map and compass: bearings and declination basics

TUREFF• •0

Phone apps are excellent until the battery dies, the screen will not respond with cold, wet fingers, or a signal drops in a valley. A map and a baseplate compass weigh almost nothing and never run out of charge. These are the core skills, and they are best practised on a familiar walk before you rely on them.

Know your compass

A walker's baseplate compass has a few key parts:

Baseplate: the clear rectangular plate, with a direction of travel arrow at one end and rulers along the edges.
Rotating housing (bezel): marked in degrees from 0 to 360, with orienting lines and an orienting arrow printed inside.
Magnetic needle: its red end points to magnetic north.

Keep the compass away from phones, metal and magnets, all of which can pull the needle off.

Three kinds of north

True north: the direction of the geographic North Pole.
Grid north: the direction of the vertical grid lines on your map.
Magnetic north: where your compass needle points, which is not the same place as the geographic pole.

The angle between magnetic north and grid north is called magnetic declination, sometimes called variation. It differs from place to place and changes slowly every year, because the Earth's magnetic field is constantly shifting. Scientific agencies publish a model of the field that is updated on a recurring five-year cycle. Your map's margin normally states the declination and how it changes; for a current figure, use an official online declination calculator from a national geological survey. In some places the difference is small enough to ignore over short distances. In others it is many degrees, which can put you hundreds of metres off course over a few kilometres.

Setting the map

Before taking any bearing, orient (set) the map so that it matches the ground in front of you. Lay the compass on the map, turn the map until the needle lines up with the grid lines pointing north, and the features on the map will now line up with the real hills, rivers and paths around you. This alone answers many "which way now?" questions.

Taking a bearing from the map

Place the edge of the baseplate along a line from where you are to where you want to go, with the direction of travel arrow pointing towards your destination.
Turn the housing until its orienting lines are parallel to the map's grid lines, with the orienting arrow pointing to the top of the map.
Read the bearing at the index mark where the housing meets the baseplate.
Adjust for declination if it matters where you are. Whether you add or subtract depends on whether magnetic north lies east or west of grid north in your area; the map margin will tell you which. A common memory aid in places with west declination is "grid to mag, add".
Take the compass off the map, hold it flat in front of you, and turn your whole body until the red needle sits inside the orienting arrow. The direction of travel arrow now points the way to walk.

Walking on a bearing

Pick a landmark on the line of your bearing, such as a boulder or a distinctive tree, walk to it, then pick the next one. This is far more accurate than staring at the compass as you go.
Measure distance using the map scale and either timing or pacing. Count how many double paces you take for 100 metres on flat ground before your trip, and expect more on steep or rough ground.
Aim off deliberately when heading for a point on a line feature, such as a bridge on a river. Aim slightly to one side, so that when you hit the river you know which way to turn.
Use handrails and catching features: walls, streams and paths that guide you, and features beyond your target that tell you when you have gone too far.

When you are unsure of your position

Stop early, rather than pressing on. Set the map, identify obvious features, and take bearings to two or three of them. Where the back bearings cross on the map is roughly where you stand. If visibility is poor, retrace your route to the last point you were certain of. What navigation trick has saved you on a hill or in the woods? Share it in the comments.