Magnetic declination is an essential principle to understand when navigating your way through
wilds with map and compass.Yet it’s a tricky thing to remember, at least way it has traditionally been taught, using an addition / subtraction method. Just when you think you’ve grasped it, concept floats away, like fog in morning light.
Well there is a simple, practical approach to adjusting for magnetic declination when finding your bearings. The whole explanation begins with a definition of ‘north.”
There are 2 Norths
A lot of people know that there are 2 norths in terms of maps and compasses. A map shows true north, or Geographic North Pole where all lines of longitude meet. The earth rotates around an imaginary axis that runs through North and South Poles.
A compass needle points to magnetic north, which is determined by earth’s magnetic field. The location of magnetic north moves over time, at about 5 miles per hour. Right now it is slowly creeping around somewhere NW of Hudson’s Bay in Canada, about 450 miles away from true north.
Magnetic Declination
The angular difference between true north and magnetic north is known as “declination,” or “variation” in aviation world. Declination is different for different parts of globe. In Washington State, angle of declination is 20°east. This means that magnetic north is 20° east of true north. In Tennessee angle of declination is 0°, and in Maine, it’s 20° west.
Declination values can be found in margins or legend on topographic maps. Because point of magnetic north is constantly moving, it is important to have a recent topo map for finding your way in woods.
A similar point to remember is that compasses are calibrated for different parts of world. So when you purchase a compass, be sure that it is intended to be used in area of your big hiking vacations.
How to Find Your Bearing
Follow these steps to find your bearing:
1. Place compass on map with arrow on base plate pointing in direction you want to go.
