There are 3 different Norths that we need to know about:
- True North - This is the direction towards the North Pole. Lines of longitude meet at the North Pole.
- Grid North - This is the direction of the North-South Grid lines on the map. As grid lines are parallel
lines not all of them can point to the North Pole. So there is a small difference between grid north and true north because
the earth is a sphere and the map is flat.
- Magnetic North - This is the direction that the compass needle points. The position of the North Magnetic
Pole varies a bit from year to year. Currently it is somewhere near Bathurst Island in the NWT (or may be Nunavut now).
The Magnetic Declination at a point on the earth's surface is the angle between grid north and magnetic north.
Somewhere on the border of most maps there is a set of arrows to indicate the relationship between the 3 norths
at a particular point on the map. Usually, there will also be a narrative like:
Magnetic North was 20 degrees east of grid north in 1976 and this angle is decreasing by 5' a year. (1'
means 1 minute or 1/60th of a degree. There are 360 degrees in a circle.)
Some examples of magnetic declination:
Knowledge of the magnetic declination is needed in order to use the compass correctly to either find your
way or identify distant mountains. Most maps and compasses have 360 degrees in the circle. However in Norway they use 400
degrees to the circle - so beware!
Taking Compass Bearings
From Map to Ground
This technique is used for finding out which way you want to go
from a known point - used for navigation in treed areas and in bad visibility conditions above treeline.
- Using a compass with no built in adjustment for magnetic declination:
- Place a corner of the compass that is closest to the string hole on your known position on the map.
- Align the long side of the compass along the direction you wish to travel.
- Rotate the circle part of the compass so that the North mark on the compass circle and the lines within it
align with the north-south grid lines on the map. N.B. The position of the compass needle and the orientation of the map are
irrelevant!
- Read off the number on the circle part of the compass by the arrow or mark towards the direction you wish
to travel. (This is the angle between Grid North and the direction you wish to travel)
- Convert this angle to a magnetic bearing by using the diagram of the 3 norths on the map: Place the compass
on the norths diagram with the N of the compass circle pointing to grid north on the diagram. Rotate the compass circle the
required number of degrees towards magnetic north on the diagram.
- Put the map away and align the compass so that the North end of the compass needle points to the North mark
on the compass circle.
- Walk in the direction to the arrow or mark on the compass - keep watching that needle!
- Using a compass with a built in adjustment for magnetic declination:
- Make sure the declination marker arrow is set correctly for the map you are using.
- Place a corner of the compass that is closest to the string hole on your known position on the map.
- Align the long side of the compass along the direction you wish to travel.
- Rotate the circle part of the compass so that the North mark on the compass circle and the lines within it
align with the north-south grid lines on the map. N.B. The position of the compass needle and the orientation of the map are
irrelevant!
- Put the map away and align the compass so that the North end of the compass needle points to the declination
marker arrow.
- Walk in the direction to the arrow or mark on the compass - keep watching that needle!
From Ground to Map
This is used for:
- Identifying unknown objects or mountains from a known point or
- Finding your unknown position on the map from 2 or more known visible objects.
Instructions
for (i) below:
- Using a compass with no built in adjustment for magnetic declination:
- Point arrow in body of compass at unknown object.
- Rotate the circle part of the compass so that the north end of the compass needle points to the north mark
on the compass circle. (Keep compass body pointing at the object)
- Read off the number on the circle part of the compass by the arrow or mark on the compass that was pointing
towards the object. (This is the angle between Magnetic North and the direction of the unknown object)
- Convert this angle to a Grid bearing by using the norths diagram on the map. Place the compass on the norths
diagram with the N of the compass circle pointing to magnetic north on the diagram. Rotate the compass circle the required
number of degrees towards grid north on the diagram.
- Get the map out. Place a corner of the compass that was nearest you when you looked at the object, on your
known position on the map. N.B. The position of the compass needle and the orientation of the map are irrelevant!
- Keeping that corner of the compass in place align the long side of the compass so that the North on the compass
circle and the grid lines in the circle align with the North-South grid lines on the map.
- The unknown object is somewhere on the line of the long side of the compass in the direction of the arrow
on the compass body. You will need to extend the line beyond the compass. The object may not be on your map!
- Using a compass with a built in adjustment for magnetic declination:
- Make sure the declination marker arrow is set correctly for the map you are using.
- Point arrow in body of compass at unknown object.
- Rotate the circle part of the compass so that the north end of the compass needle points to the north end
of the declination arrow of the compass. (Keep compass body pointing at the object)
- Get the map out. Place a corner of the compass that was nearest you when you looked at the object, on your
known position on the map. N.B. The position of the compass needle and the orientation of the map are irrelevant!
- Keeping that corner of the compass in place align the long side of the compass so that the North on the compass
circle and the grid lines in the circle align with the North-South grid lines on the map.
- The unknown object is somewhere on the line of the long side of the compass in the direction of the arrow
on the compass body. You will need to extend the line beyond the compass. The object may not be on your map!
