How to Use a Compass with a Map
Baseplate, bezel, magnetic needle — what the parts do, how to set declination once for the whole trip, and the three-step routine for staying on course.
A compass paired with a paper map is the navigation skill that works with dead batteries. Learn its five parts, set the declination once before the trip, then: orient the map to the land, measure a bearing to your target, and follow it from landmark to landmark. Cross two or three bearings on known landmarks and you can pinpoint exactly where you stand.
A compass is one of the ten essentials. Together with a paper map, it is the basic navigation ability that doesn't depend on electronics.
The Anatomy
- Baseplate: transparent, so you can see the map beneath it; the straight edge is for measuring direction.
- Bezel: the rotating ring marked with 360° — also called the azimuth ring.
- Direction-of-travel arrow: points where you want to go.
- Magnetic needle: the red end always points to magnetic north.
- Orienting arrow: you align the magnetic needle inside it to establish north.
Declination: True North vs. Magnetic North
The north on your map is true north; your needle points to magnetic north. The angle between the two is declination. In the continental US it swings from about 20° east in Washington State to 20° west in Maine. In China it runs roughly 5–10° west in the east and 0–5° east in the west.
Look up the local declination before you set out, adjust the compass once, and you won't have to touch it again for the whole trip.
Using It in the Field
Step 1: Orient the map. Set the compass on the map with the direction-of-travel arrow pointing to the top of the map. Turn the bezel so N lines up with the arrow. Slide the baseplate until its straight edge aligns with the map's edge, running north–south. Now rotate your body until the magnetic needle sits inside the orienting arrow — the map now matches the terrain around you.
Step 2: Take a bearing. Find your current position and your target on the map. Lay the compass's straight edge from where you are to where you're going. Rotate the bezel until the orienting lines are parallel with the map's north–south lines. Read the degrees at the index line — that is your bearing.
Step 3: Follow the bearing. Hold the compass level with the direction-of-travel arrow pointing ahead. Turn your body until the magnetic needle sits inside the orienting arrow. The arrow now points at your target. Pick a distinct landmark along that line, walk to it, and repeat.
Triangulating Your Position
Off a known route, you can fix your position by crossing bearings:
- Find two or three landmarks you can identify both on the map and in the field.
- Take a bearing to each of them.
- On the map, draw a line back from each landmark along the reverse bearing.
Where the lines intersect is where you stand.