Compass types

Good compasses have a fluid-filled housing; the fluid dampens the motion of the needle, so that you can use the compass without holding it perfectly still. Avoid inexpensive compasses that do not have fluid-filled housings. The compass needle is painted in two colors. Assuming that the compass is held flat, the red end points to north, and the white end to south. An interesting detail is that there are northern- and southern-hemisphere compasses. This has to do with the fact that the magnetic field lines, to which a compass needle aligns, point into the earth at the north and south magnetic poles. In the northern hemisphere the north end of the needle is pulled downwards, and the south end is counterweighted to balance the needle. When you use a northern hemisphere compass in, say, Australia, the south end of the magnet is pulled downwards by the magnetic field, and is also heavier than the north end - resulting in a needle that catches and drags on the bottom of the compass housing when the compass is held horizontal.
A good compass will last a long time. However, some things can go wrong with a compass: the plastic components can break, or the housing can develop a leak. Over time, the fluid within the housing may turn an opaque blue-green. And, very rarely, the magnetization of the compass needle may reverse, so that the south end now points to north.

There are two main types of orienteering compasses:

The baseplate or protractor compass

This type of compass was invented by the Kjellstrom brothers during the World War II era and consists of a rectangular baseplate, which is marked with a red arrow pointing along the long axis, and a rotating compass housing marked in degrees (360 degrees for the full circle in most of the world, but 400 on some European compasses). Marked on the floor of the rotating compass housing are an arrow and a set of lines parallel to that arrow. Additional features may include a lanyard for attaching the compass to the wrist, scale bars for measuring map distances along one or more edges of the baseplate, a magnifying glass for reading fine map detail, and templates of a circle and triangle for marking orienteering courses on the map.

The thumb compass

In the mid 1980s, a top Swedish orienteer developed an alternative to the baseplate compass by reshaping the baseplate and adding a strap for attaching the compass to his thumb. This compass is then placed on the thumb of the left hand, which holds it on the map. The advantage of this system is that the map and compass are always read as a unit, the map is aligned more easily and quickly, plus one hand is left free; the disadvantage is that running very accurately on a bearing is more difficult. Personal preference usually determines the type of compass that is used; world championships have been won using both types.

Using either type of compass, there are two basic skills an orienteer needs:

orienting the map
taking a bearing.

Using a compass for orienting the map

This is a simple skill, and is probably the most important use of the compass:
Hold your map horizontally.
Place the compass flat on the map.
Rotate the map until the "north lines" on the map (a series of evenly spaced parallel lines drawn across the map, all pointing to magnetic north) are aligned with the compass needle.
The map should now be oriented to the terrain. This makes it much easier to read, just as text is easier to read right side up than upside down.

Taking a bearing

Every direction can be expressed as an angle with respect to north. In the military and the boy scouts, this is called an "azimuth", and bearings are expressed as a number of degrees. Orienteers take the easy way out, just setting the angle on their compass and keeping the needle aligned, which in turn keeps them going in the right direction. A simple set of step-by-step instructions for setting a bearing on a baseplate compass are:
place the compass on the map so that the direction of travel arrow is lined up with the way you want to go
turn the compass housing so that the arrows engraved in its plastic base are parallel to the north arrows drawn on the map (make sure the arrowhead points north and not south)
take the compass off the map and hold it in front of you so that the direction of travel arrow points directly ahead of you
rotate your body until the compass needle is aligned with the arrow on the base of the compass housing
pick out a prominent object ahead of you along the direction of travel, go to it, and repeat the process (this way you can detour around obstructions but still stay on your bearing)

How important is the compass?

The most important navigational aid used in orienteering is the human brain. One other navigational device is in allowed and in general use: the compass. Compasses are useful for taking bearings and for orienting the map so that it is aligned with the terrain - but it is possible, in most areas, to complete a course quite easily and efficiently without a compass (an exception: it would be difficult to navigate flat areas poor in prominent features without a compass).

The compass is the only legal navigational aid that can be used in orienteering. Altimeters are specifically prohibited and GPS units are implicitly prohibited by the rules. It has been stated that GPS units could be very useful and helpful aids, but when the question of how an everyday orienteer would use a GPS unit to defeat the reigning US champion in a race was raised, the only valid reply was: "I would wait at the first control for him, use the GPS unit to knock him out, and then proceed on to victory". Technology, however powerful, is no match for basic navigational ability - even in the hands of a good orienteer who is also a technological wizard. Beginning orienteers should learn basic compass skills and work on mastering map reading.

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