Compass
Using a Baseplate Compass for Field Bearings
A baseplate compass, the clear rectangular type with a rotating bezel, does two jobs: it measures the direction of a line drawn on a map, and it lets you hold that same direction while walking. Everything below assumes that tool and a paper map.
Taking a bearing from the map
- Lay the long edge of the baseplate along your intended line, with the direction-of-travel arrow pointing from where you are to where you want to go.
- Rotate the bezel until its orienting lines are parallel with the map's north–south grid lines, and the orienting arrow points to map north.
- Read the bearing at the index line. This is your map bearing, measured against grid north.
Declination matters in Canada
Magnetic north and true (or grid) north differ by an angle called declination, and that angle changes with location and slowly over time. Across Canada it varies widely, and in some regions it is large. Always check the current declination for your area, shown in the map margin or available from official sources, and apply it before you trust a bearing in the field.
Applying declination
If your compass bezel does not have an adjustable declination scale, you correct by hand. The principle: convert between the map bearing and the bearing you actually steer by adding or subtracting the local declination. Work it out once for your area, write it on the map, and apply it the same way every time, consistency prevents the classic error of correcting in the wrong direction.
Following the bearing
With the bearing set, hold the compass flat in front of you and turn your whole body until the magnetic needle sits inside the orienting arrow, the common phrase is "put the red in the shed." The direction-of-travel arrow now points where you want to go.
Rather than staring at the needle as you walk, pick a distinct object ahead that sits on the line, a particular tree, a boulder, a break in the canopy, walk to it, then sight the next one. This keeps you straight over ground where you cannot see the destination.
Two techniques that absorb error
- Aiming off: when navigating to a feature on a line, such as a control near a stream, deliberately aim to one known side. When you hit the stream you know which way to turn, instead of guessing.
- Attack points: navigate first to an easy, unmistakable feature near your target, then take a short, careful bearing for the final stretch where precision counts most.
| Term | Meaning |
|---|---|
| Index line | Where you read the bearing on the bezel |
| Orienting arrow | The "shed" the needle must sit inside |
| Declination | Angle between magnetic and true/grid north |
| Aiming off | Deliberate offset to a known side of a target |
Used together, a clean map bearing, correct declination, and a sighted line will put you within reach of small features even in featureless or low-visibility ground.