Compass and Map - part 1

Articles In This Section:

· Compass and Map - part 1

· Compass and Map - part 2

· Compass and Map - part 3

· Compass and Map - part 4

· Compass and Map - part 5

· Compass and Map - part 6

Many are the tales of successful escape from disaster by storm, made possible by reliance upon a so-called sense of direction, or upon the legend that moss always grows on the north side of trees. The skier, however, should bear in mind that there are perhaps many more tales of failure to escape disaster which never have been told, and, indeed, never can be. Bearing this in mind, he should acquire an adequate knowledge of the proper use of compass and map, and rely on this knowledge—and not on superstition—when he is required to travel with visibility poor or in country that is new.

Magnetic declination.—The angle between the direction in which the compass needle points and true geographic north is known as the magnetic declination. The needle is aligned with the strongest lines of magnetic force affecting it. In the absence of such magnetized objects as a knife, ice ax, steel pole, or local beds of magnetic ore, the needle will always point approximately toward the north magnetic pole of the earth. This is on Boothia Peninsula, about 1300 miles south of the geographic north pole. Consequently, at about Cincinnati, magnetic north and true north will be in line. East of Cincinnati the compass needle will point west of true north; west of Cincinnati it will point east. A clear understanding of this will show how declination varies, and why one cannot rely upon declination marked upon a compass, which may be made in France but used in British Columbia.

Conversion of compass readings.—The amount and direction of declination is nearly always shown on better maps. To obtain a true map reading where there is an east declination, add the amount of the declination to the compass reading; in localities having west declination, subtract the amount. In the field it is usually simplest to use magnetic bearings throughout, since no conversion is then necessary.