Natural Navigation

1 – WildlifeCampus Wilderness Navigation Course

Module 3 - Component 1

What is Direction?

What is Direction? This course material is the copyrighted intellectual property of WildlifeCampus. It may not be copied, distributed or reproduced in any format whatsoever without the express written permission of WildlifeCampus.

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Introduction

“If we don’t change direction soon, we’ll end up where we’re going. ”

Professor Irwin Corey (1914 - 2017)

Arriving at the right place at a reasonable time by an efficient route is the essence of the outdoor traveller’s navigational aims. Direction plays an important role in all travellers’ everyday lives. This component contains the basic definitions of navigation and the three different common base lines for north.

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Base Lines

In order to measure something, there must always be a starting point or zero measurement. To express direction as a unit of angular measure, which is what we need, there must be a starting point and a point you are measuring to. The starting point is the base or reference line. There are three common base lines: true north, magnetic north, and grid north. The most commonly used in navigation are magnetic and grid.

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True north

True north is a straight line from any point on the Earth’s surface to the North Pole. All lines of longitude (the ones going up and down) are true north lines and meet at the North and South Poles. North is usually symbolised by a line ending with an arrowhead or star. This is NOT where your compass is pointing…

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Magnetic north

Magnetic north is the northern magnetic pole of the Earth. This IS where your compass is pointing, the direction to the northern magnetic pole. Magnetic north is usually symbolised by a line ending with a half arrowhead. It is actually not a single small place like the true North Pole but in fact a large area of intense magnetism. This could be either to the left (west) or right (east) of true north, depending on where on the world’s surface you are.

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Grid north

The north (base line) that is established by using the vertical grid lines on the map is grid north. It is commonly thought of as being true north and for all intents of purpose, this is okay when working on a single map, but in fact, due to the curvature of the Earth and that meridians curve towards the North and South Poles, there is a very slight difference between grid north and true north. Grid north may be symbolised by the letters GN. Unless your map has had a custom grid drawn on it that is not based on true north you can generally ignore the difference between grid and true north. Check the notes on your map.

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Magnetic Declination and Mean Annual Change

The angular difference between magnetic north and true north is known as the magnetic declination or variation. For ease of reference when using a compass, we always calculate the magnetic declination to the nearest degree. As the magnetic declination is not constant, due to what is known as the mean annual change (shift), always check with the figures given in the margin of your map.

The declination diagram on a map shows the angular relationship, represented by prongs, between the grid, magnetic, and true North’s. While the relative positions of the prongs are correct, they are seldom plotted to scale. Do not use the diagram to measure a numerical value using a protractor. The value will be written in the map margin beside the diagram. The prongs simply indicate a west or east declination.

TN TN

MN MN

Declination West or East of True North

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On some older maps, the magnetic declination information was confusing because it was represented as degrees and points of a degree. So 10º 0.5 west actually meant 10º 30’ west (10 degrees 30 minutes), and not 10º 5’ west. This caused complications in calculating the magnetic declination as 10º 0.5º minus 3’ involved a lot of thought. On newer maps, the declination information is given in degrees and minutes so it will be easy to calculate 10º 30’ minus 3’ (= 10º 27’).

The symbols º,’ and ” represent degrees, minutes and seconds respectively. (we will cover more on this when we look at grids.) It is critically important to check the notes on your map to determine if magnetic north is west or east of true north, based on where you are, as this makes a big difference.

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Maps will also tell you what the mean annual change is. For example, the map could state:

Declination was 19.8° west in 1987, and the mean annual change is 1’ eastwards per year.

19.8° is the same as 19° 48’. At a 1’ easterly movement each year, and there being 23 years (till 2010) since the map was compiled means we subtract 23’ from 19° 48’, making a present time declination of 19° 25’. So calculating to the nearest degree in 1987 the magnetic declination would have been 20° east of true north, but in 2010 it is 19°. We always use the closest whole degree when working out declinations. Check the map date you are using, and only do the conversion if it is really old.

Looking at another example, the map states:

Declination was 10° 5’ east in 2000, and the mean annual change is 1’ eastwards per year.

At an 1’ east movement each year, and there being 10 years (till 2010) since the map was created means we add 10’ to 10° 05’ (as we measure clockwise), making a present declination of 10° 15’. So in 2000, the magnetic declination would have been 10° east of true north, and in 2010 it is still 10°. (Working to the closest degree) In some places on Earth, magnetic and true north are aligned so no conversion is necessary.

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Methods of expressing direction

“The only reason some people get lost in thought is because it’s unfamiliar territory.”

Paul Fix

Travellers need a way of expressing direction that is accurate, adaptable to any part of the world, and has a common unit of measure. Directions referred to by the common ‘left’ or ‘right’ are all very well but are not suitable for the outdoor environment, so direction is rather referred to as units of angular measure which are called ‘azimuths’, more commonly known as ‘bearings’.

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Azimuth or Bearing

The word ‘azimuth’ comes from an Arabic form of a Latin word meaning way or path. This is the direction of an object, measured clockwise around the observer’s horizon from a base line. The common term ‘bearing’ is in fact probably incorrect as a bearing, or to use the correct term, ‘surveyor’s bearing’, divides a circle into four segments of 90 degrees, and to read a position using the surveyor’s bearings, you first identify the base direction line and then record the angle east or west of that line, followed by the direction east or west of that line. For example North 30° West (30° west of north.) A surveyors bearing can never exceed 90°.

North North 30 degrees West

North 45 degrees East

West East

South 80 degrees East

South 22 degrees West South

This is awkward for walking navigation, so we use a term called the azimuth or bearing. An azimuth is the angle measured between you, an object and a base line, and is measured from the true base line (north), clockwise around a circle back to the base line. However there is little consensus worldwide on the terms ‘azimuth’ and ‘bearing’ with many differing explanations given.

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Some of these include:

Azimuth refers to direction from true north clockwise. Bearing is the direction from grid north or south also clockwise. In South Africa, bearings are measured from 0 degrees south. Aslam Parker, Deputy Director: Professional & Scientific Services: Surveys &

Mapping South Africa’s National Mapping Organisation

Azimuth: A horizontal angle reckoned clockwise from the meridian. Bearing: in general the horizontal angle between a line from the observer to a given point. Geodetic Glossary of the National Oceanic and Atmospheric Administration (USA) http://www.noaa.gov

Azimuth is particularly applied to directions determined by astronomical means and is the clockwise angle between a line to the point in question and the direction to the North Pole. Bearing is particularly applied when referring to an initial direction that is related to the direction of the grid lines on the map. Jim Smith, Honorary Secretary of the International Institution for the History of Surveying and Measurement UK

Bearings are deemed to be true geographical angles of direction and are related to true north or true south… the word ‘bearing’ should thus not be used when dealing with a rectangular co-ordinate system – that is, the ellipsoidal latitude and longitude co-ordinates projected on a plane surface {maps}. It seems to be advisable to use the term ‘grid bearing’ when referring to a projection {map}; the term ‘true bearing’, ‘astronomical bearing’ or ‘azimuth’ when referring to true north or true south, and ‘magnetic bearing’ when referring to magnetic north. Tomasz Zakiewicz, Deputy Chief Land Surveyor, Directorate: Surveys and Mapping

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However for the purposes of this course, we will use the term ‘bearing’ for all references to a direction for ease of reference, and I quote J.R. Smith in his Introduction to Geodesy when he says,

“… while it is preferable for all nations to use the same definitions and terminology, it is a fact of life that neither these nor some other survey terms are universally exclusive, and so should be interpreted in the context of the publication in which they appear.”

Should you prefer to use the term ‘azimuth’, go ahead. There are three possible ways of expressing the direction1 in which we wish to go in:

1 The term direction is also strictly incorrect, but we will not go into that here…

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Azimuth

True bearing (azimuth)

The angle determined if the North Pole (Earth’s rotational pole) is used as the base line reference point clockwise to a point.

Magnetic bearing (azimuth)

The angle measured with the magnetic North Pole as the base line and determined by using magnetic instruments, for example, a magnetic compass.

Grid bearings (azimuth)

The angle determined if the top of the map’s grid is used as the base line reference point clockwise to a point. There are many ways in which to measure this angle, but the four common units used are degrees, milliradian, grad and points.

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Degree

The most common unit of measure is the degree (°) subdivided into minutes of angle (MOA) (’) and seconds of angle (SOA) (”).

1 degree = 60 minutes (1° = 60’)

1 minute = 60 seconds (1’ = 60”)

There are 360 degrees in a circle.

The degree is the preferred unit of measurement for common navigational use, but it is interesting to know about some others.

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Milliradian

Another unit of measure, the milliradian or mil, is used mainly in military gunnery but ‘mil’ does not stand for military. The mil expresses the size of an angle formed when a circle is divided into 6,400 angles with the vertex of the angles at the centre of the circle. If the circle has a radius of 1,000 yards, one mil would relate to one yard on the circumference of the circle.

0 Milliradian Also 6,400 Mils

4,800 Mils 1,600 Mils

3,200 Mils

This allows for easy determination of range and angle for setting the sights on artillery weapons. A relationship can be established between degrees and mils.

A circle equals 6,400 mils divided by 360 degrees, or 17.78 mils per degree.

To convert degrees to mils, multiply degrees by 17.78. Using mils for general land navigation is difficult as most people battle to be accurate to one degree, let alone 17 times smaller. For normal compass work, the increments are simply too small.

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Grad

The grad is the unit of measure found on some maps (this is also known as gon, grade, or gradian). There are 400 grads in a circle (a right angle equals 100 grads).

0 Grad Also 400 Grad

300 Grad 100 Grad

200 Grad

The grad is divided into 100 centesimal minutes (centigrade) and the minute into 100 centesimal seconds (milligrads). The metric grad system has never been popular with walking-based navigators.

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Points

Points or cardinal points were used to express direction before the invention of the magnetic compass, although you will still often hear the terms used.

North

North NE (To the North of North East)

NE (To the North East)

East NE (To the East of North East)

East

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A ‘point’ is defined as one eighth of a right angle. Therefore, it equals exactly 11.25 degrees. For example, a bearing of northwest by north differs by one point from a north-west bearing, and by a point from a north-northwest one.