A compass points to magnetic north; but this may not be the same as grid north, which depends on your locality. If you live close to the imaginary line that runs from Thunder Bay through Savant Lake, in northern Ontario, northwest through Churchill, Manitoba, you're in luck. Here your compass north is approximately the same as grid north. But if you live east of this line, your compass points off to the west, while west of that line it points off to the east. The reason is that the North Magnetic Pole, which attracts the compass needle, is situated at 81.3° N, 110.8° W (2001). Visit the Geological Survey of Canada's Canadian National Geomagnetism Program website for more information about the North Magnetic Pole.
Compasses are available in many forms. The simplest is the common needle compass, which consists of a magnetic needle held free to rotate over a compass card. Remember, when the needle comes to rest, it is pointing at magnetic north. Turn the compass gently under the needle until north on the card lies under the north end of the needle. Magnetic directions are then indicated by the card. More expensive compasses, such as prismatic and orienteering compasses, have additional features that make it easier to read directions. Instruction booklets for these compasses should be obtained from the dealer.
Finding Compass Bearings and Grid Bearings
To find grid bearings you must know how far off grid north the compass points in your locality. Look in the margin of your topographic map for the compass declination. The rhyme to use is:
Declination East - Magnetic least (i.e. magnetic less than grid)
Declination West - Magnetic best
As an example, in Ottawa the compass points off to the west (declination west) about 13°. So according to the rhyme, a magnetic bearing is greater than a grid bearing.
