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Map & Compass Basics

Posted by Coondog on 23 March 2012

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If you've done one of our Into the Wild courses, you would've spent some time looking at basic navigation techniques using a map and compass. This can be a confusing topic for some - especially when throwing around words like magnetic declination and map topography. The reality is, it's quite a simple process once you get your head around it - particularly now, with some much simpler teaching methods to adjust for magnetic declination. Anyway, as a reminder for those who've done the course and as a simple reference for others, we thought a blog on the topic could be helpful. You'll need to have some basic knowledge on how to read a topographic map for this to make sense - and in New Zealand, the best maps to use are the new(ish) Topo50 maps put out by Land Information NZ (LINZ).

How to...

A: Take a bearing from a map

1. Place the compass on the map with the edge of the compass along the desired line of travel.

2. Rotate the compass housing until N on the dial points North on the map. Check that the compass housing north/south lines (these are coloured red/black on Silva compasses) are parallel with the vertical grid lines on the map (called meridians). Read the bearing at the direction of travel arrow.

3. Hold the compass in your hand and turn yourself until the red end of the compass needle (North) points to the magnetic variation on the adjustable dial (somewhere around 22-23˚ for New Zealand depending on where you are*). The front of the compass with the direction of travel arrow is now pointing towards your destination.

Silva's 1-2-3 System

B: Find a bearing for a physical feature in landscape

1. Point direction of travel arrow towards physical feature (eyeballing), then turn the adjustable dial until the red end of the compass needle (North) points to the magnetic variation*.

2. Read the bearing at the direction of travel arrow. Place compass on the map with the edge on your known location (or on the known feature) and rotate the entire compass until N on the dial points North on the map (don’t adjust the housing). Check that the compass housing north/south lines are parallel with the vertical grid lines on the map.

This technique can be used to find out your location (using triangulation) if you know where the feature is on the map, or if you know your location, where the feature is on the map.

* Note: For general use a line can be marked on the dial between 20˚ (easily remembered and sufficiently accurate for most purposes) and the pivot to make it easier to keep the needle in the right position. On some of compasses you can set an adjustable indicator line to the variation. Also, if you want to be really accurate, on most topographical maps the magnetic variation for your particular area can be found on the bottom left corner of your map.

Navigation Trivia:

Magnetic North vs. True North:

A compass points towards magnetic north, but this is not the same as true north. Sound confusing? Magnetic north is the direction the needle of the compass points to. This direction is based on the magnetic fields of the earth and is not the same as true north, which is the geographic north or toward the North Pole. In New Zealand magnetic north is actually around 23˚ east of true north (varies from one end of the country to the other). This is known as magnetic declination.

Global Magnetic Regions:

Because of the Earth’s curvature and variances in the Earth’s magnetic field, a compass designed for the northern hemisphere will ‘stick’ in the southern hemisphere, as it will basically be trying to point towards the ground.

The image below shows the 5 magnetic zones the compass industry has defined. Depending where in the world you are, any standard compass you purchase generally has its needle balanced only for that region. e.g: most compasses sold in New Zealand will only be most effective in New Zealand and Australia. Our zone (Zone 5) is generally shown on the base of the compass as the code MS.

Magnetic Zones of the World

Now what?

The best thing you can do now, is grab a map and compass, and get out there and practice! Find a topo map for the area you live in (it's even better if you live around hills or prominent landmarks) and give these instructions a go. As they say ... practise makes perfect!

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