Compass Directions and Bearings
Direction sounds like the simplest thing on a map, right up until you notice your compass and your map disagree about where north is.
The compass rose
The compass rose is the little star printed on a map showing which way is which. At its simplest it has four points, the cardinal directions: north, east, south and west. Add the intercardinals and you get eight: northeast, southeast, southwest, northwest. Add another layer and you reach the sixteen-point rose, with names like north-northeast, which is the level of precision most people ever need in words.
Beyond sixteen points, words stop being useful and everyone switches to degrees. That is what a bearing is.
Bearings: direction as a number
A bearing is a direction expressed as an angle from 0 to 360 degrees, measured clockwise starting at north. North is 0 (or equivalently 360), east is 90, south is 180 and west is 270. Everything in between gets its own number, so a bearing of 247 degrees is unambiguous in a way that "roughly west-southwest" is not.
Bearings are always given as three digits, including leading zeros, so due east is written 090 and not 90. That convention exists because it removes any doubt about whether digits were lost in transmission, which matters when the bearing is being read aloud over a radio.
How to take a bearing from a map
This is the classic compass-and-map procedure, in the order it is actually done.
- Line up the compass edge Place the long edge of the compass baseplate along the line from where you are to where you want to go, with the direction-of-travel arrow pointing the way you want to move.
- Turn the housing to match the map Rotate the compass housing until the orienting lines inside it are parallel with the north-south grid lines on the map, with the housing arrow pointing to map north.
- Read the bearing Read the number at the index line on the housing. That is your grid bearing.
- Adjust for declination Add or subtract the local magnetic declination to convert the grid bearing into a magnetic bearing that your needle will actually agree with.
- Walk it Hold the compass level in front of you and turn your whole body until the needle sits inside the orienting arrow. The direction-of-travel arrow now points where you are going.
Three different norths
This is the part that catches people out. There is more than one north, and they do not agree.
True north is the direction of the geographic North Pole, where all the lines of longitude meet. Grid north is the direction the vertical grid lines run on your map, which is very slightly different from true north almost everywhere, because a flat grid cannot align perfectly with curved meridians. Magnetic north is where a compass needle actually points, and it is somewhere in the Canadian Arctic, drifting a few tens of kilometres a year.
The angle between true north and magnetic north is called magnetic declination, or sometimes magnetic variation. It depends on where you are standing and it changes over time, which is why maps print both the value and the year it was measured.
Worked example
Your map gives a grid bearing of 072 degrees. The declination is 14 degrees west. What bearing do you set on the compass?
- Declination west means magnetic north sits west of grid north
- For a westerly declination, add it to the grid bearing
- 072 + 14 = 086
Set 086 degrees on the compass. The old mnemonic is "west is best, east is least": add a westerly declination, subtract an easterly one.
Check what you learned
Five questions on direction and bearings. Pass at 70% or better to complete the lesson.
Practice with Games
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Compass directions, in one paragraph
The compass rose on a map shows which way is which. Its four cardinal directions are north, east, south and west; adding the intercardinals gives eight points, and a further subdivision gives the sixteen-point rose. Beyond that, direction is expressed as a bearing: an angle from 0 to 360 degrees measured clockwise from north, written with three digits so due east is 090. There are three different norths to keep straight. True north is the geographic pole, grid north is the direction of the vertical lines on your map, and magnetic north is where a compass needle points. The angle between true and magnetic north is the magnetic declination, which varies by location and drifts over time, so a bearing taken from a map must be adjusted before a compass will agree with it.
Common questions about compass directions
What are the four cardinal directions?
North, east, south and west. In degrees they are 0, 90, 180 and 270, measured clockwise from north. The four points between them, northeast, southeast, southwest and northwest, are called the intercardinal or ordinal directions.
What is the difference between true north and magnetic north?
True north is the direction of the geographic North Pole, where the lines of longitude converge. Magnetic north is where a compass needle points, currently in the Canadian Arctic and moving steadily. The angle between them is the magnetic declination, and it differs depending on where in the world you are standing.
How do I take a bearing with a compass and map?
Lay the compass edge along your intended route with the travel arrow pointing forward, rotate the housing until its orienting lines are parallel to the map grid with the arrow pointing to map north, read the number at the index line, then adjust for local declination before following it.
Do I add or subtract magnetic declination?
Going from a grid or true bearing to a magnetic one, add a westerly declination and subtract an easterly one. The usual mnemonic is "west is best, east is least". Reverse it when converting a magnetic bearing back to a map bearing.
Is north always at the top of a map?
By convention, usually, but not reliably. Tourist maps, transit diagrams and many historical maps are oriented differently, sometimes deliberately. That is why maps carry a compass rose or north arrow, and why checking it takes less time than getting lost.