Direction, north and bearings

A topographic map can carry three different norths, and a compass needle follows only one of them, magnetic north.

Which way is north?

Most maps are drawn with north at the top, and they show it with a north arrow. But surveyors distinguish three norths, and the NGII explains all three. True north points along the meridian to the geographic North Pole. Grid north is the direction of the vertical grid lines printed on the map, which follow the map projection and so can lean slightly away from true north. Magnetic north is the direction a compass needle settles in. The small angles between them have their own names: between true and grid north, between grid and magnetic north, and between true and magnetic north.

Magnetic declination

The angle between magnetic north and true north is called magnetic declination, or magnetic variation. NOAA’s National Centers for Environmental Information, which publishes the World Magnetic Model with the British Geological Survey, gives the rule: declination is positive when magnetic north is east of true north and negative when it is west. It changes from place to place and from year to year, because Earth’s magnetic field slowly changes. The North Magnetic Pole was found in northern Canada by James Clark Ross in 1831 and has been moving toward Russia ever since, at about 55 kilometres a year in 2007. In the latest annual report on the World Magnetic Model (2025), its average speed over the past year was about 36 kilometres.

Because declination changes, the declination diagram on an old map can be out of date. NOAA offers a calculator that gives the current value for any place and date. The correction itself is simple addition. To turn a compass reading into a true bearing, add the declination, counting west as negative. With a declination of 8 degrees west, a magnetic bearing of 100 degrees becomes a true bearing of 92 degrees.

Bearings: directions as numbers

Words like northeast are fine for conversation, but they are vague. A bearing turns a direction into a number: the angle measured clockwise from north, from 0 to 360 degrees. North is 0, east 90, south 180 and west 270. Northeast sits halfway between north and east at 45 degrees, and southwest at 225. To go back the way you came, add 180 degrees to your bearing, or subtract 180 if the number is already more than 180. A walker heading out on a bearing of 60 degrees returns on 240.

In the scene, the readout calculates the bearing from A to B with map north at the top. Try to predict it before you click. Put B straight above A and you should see a bearing near 0 degrees. Put B to the lower left and the number should land between 180 and 270. The grid lines in the scene are exactly north-south and east-west, so here grid north and true north are the same.