Which way North?

This post deals with finding North in the Northern Hemisphere.

There are 3 Norths that we need to know for navigation:

1) Grid North: This is the direction of the grid line that aligns with the central meridian on the Nation Grid, which is based on the Transverse Mercator projection.
2) True North: This is where the longitude lines meet up with the North pole.
3) Magnetic North: This is the North that compasses align to. Unfortunately this north doesn't sit still. It moves at a variable rate.

If that wasn't bad enough, North and South actually switch positions every few hundred thousand years - let hope we don't experience that one!

Using Grid North and Magnetic North

So when navigating by map and compass, we need to find what's called the magnetic declination. The declination is the angular difference between Grid North and Magnetic North. To account for this, your compass will need to be adjusted. First though, ensure that you have adjusted your compass to match Grid North on your map.

To find out your declination, you can look at your map, which should state the declination for the year that it was produced and give you an idea of how that declination changes each year, normally between 1/2 and 1 degree per year. Another way is to check a website like this one at Magnetic-Declination.com. It will grab a location from your IP address, but you can enter in your location and country to get a better idea.



As we can see on the screenshot above, I have a magnetic declination of just over 2 degrees West. Therefore I need to adjust the compass using the following rhyme: "West is best, East is least".

Therefore if the declination is West, as in the example above, add this to the compass reading when going from the map to reality. If it was East we'd subtract the value from the compass reading. This is because we're going from Grid to Magnetic.

If we had the reading from the ground (reality), we'd reverse this when going to the map. Subtracting west declination and adding east declination. This is because we're going from Magnetic to Grid.

So to say this a different way:
West Declination: Map to compass = Add. Compass to map = Subtract.
East Declination: Compass to map = Add. Map to compass = Subtract.

Finally here's a handy mnemonic to help remember which way the calculation goes:
"Empty sea, add water"
Which becomes: MTC (Map to compass), add West.

Using True North

If you don't happen to have a map and compass, then there are a couple of ways to find True North.

The first is with a watch with an analogue watch face.
1) Ensure that the watch is at the correct time. Point the hour hand to the direction of the sun.
2) Half the angle created by the hour hand and 12 (1 during daylight savings).
3) The position between the hour hand and 12 becomes South. For example the bisected angle between the sun hour hand of 8 and the position of 12 is 10. Therefore the direction of 10 is South.
4) Follow the line from South across the watch face and this is North. In the same example as above, if 10 is South, then 4 is North.

If you don't have a watch, or it's not at the correct time, then we can use a stick to find North.
1) Stand a stick in the ground.
2) Mark the spot at the end of the stick shadow created by the sun.
3) Wait 15 minutes (or what feels like 15 minutes if you don't have a device to tell the time!) Mark the spot at the end of the stick shadow created by the sun.
4) Draw a straight line between the East and West points. Stand with your first mark to your left and the second to your right. This is approximately True North.