Lecture

Leading Cadet Training

Basic Navigation

1Basic NavigationMap and Compass

Basic NavigationBasic navigation is –

Knowing where you are on the map.

Knowing where you want to get to.

Finding the best route to get there.

Good navigation is a combination of:

Good Map Reading Skills.

Good Compass Work.

Remember lines of Latitude and Longitude from your First Class Training ?

True or Grid North ?

Lines of Latitude get closer

as they approach the North and South Poles.

Grid Lines differ in that they cover a flat surface (i.e. the Map)

Because of this, Grid Lines don’t actually point

to the North Pole (True North)

Instead they are said to point to an

imaginary point called

Grid North

Magnetic North

The Earth has its own magnetic field,

so a free moving needle aligns itself with this field. This needle will always point in a north/south direction.

UNFORTUNATELY

the magnetic north pole

does not coincide with

the geographical north pole

(true north).

Magnetic NorthMagnetic North is in Canada.

In the UK Grid North is about 5o East of True North.

The other problem is,Magnetic North changes its position over time !

Magnetic North True North

UKGrid North

Magnetic North

So when navigating on a map we use

Grid North

Magnetic Variation is different across the world.

In some areas it is east of true north.

So Magnetic Variation must alwaysbe allowed for when using a map and compass for navigating.

To help, magnetic variation is always

displayed on the bottom of an OS Map.

Magnetic Variation

Magnetic Variation

Magnetic North

UKGrid North

True North

Because all compass references are made to either Grid North or Magnetic North, the angular difference between these 2 north's must be known.

This angular difference is called the Grid Magnetic Angle (GMA)

The GMA is displayed on every OS Map in the centre of the top margin.

Magnetic Variation

Magnetic Variation

Magnetic North

UKGrid North

True North

Grid-MagneticAngle

Summary

True North and south are at the geographical poles.

Grid North is the direction to which all Ordnance Survey Maps are oriented.

We take our map bearings using Grid North.

Magnetic North is the direction a compass points to,

and in the UK it is located approximately 5º West of Grid North.

Orientate Your MapAlign your map with your surroundings,

using identifiable features.

Hill

Island

River

Church

Woods

Orientate Your Map

Old walledenclosure

Re-entrant at base of slope

Shoulder on asteep slope

Stream junction

You arehere

Align your map with your surroundings,

Orientate Your MapSet the GMA against the direction of travel arrow of your Compass.

Put the compass on the mapand align the North-Southgrid lines.

Turn map & compass TOGETHER until the needle fallsinside the orienting arrow – red end pointing North.

If you cannot set the map

using observable features

you can set it with your compass.

Finding NorthIf you find it difficult to set your map using

features on the ground, it may help to know where North is.

Without a compass however, determining North is a bit tricky.

You can get a rough idea of where North is by using one of the following methods…..

Finding North

In the northern hemisphere the North Pole is indicated by the position of the Pole Star. First find the Great Bear or Plough.

Find the two ‘pointer’ stars and follow them for a distance of four timestheir separation.

And there you find the Pole Star

1. The Pole Star

Finding North

If you can see the Sun,hold your watch with the hour hand pointing at the sun.

Half the angle between the 12 o’clock position andthe hour hand points South.

If you have a Digital watch,draw a diagram showing the correct time, and use that instead.

2. Using a Watch

Due South.

Finding North

3. The Shadow MethodPlace a stick in the ground and mark the end of its shadow.

Wait for 10 to 15 minutes,and then,Mark the end of the new shadow.

A line between the marksruns roughly west to east.

East

West

Check of UnderstandingWhat is navigation all about?

Establishing your height above sea level

Checking your position against GPS

Finding your latitude and longitude

Knowing where you are on a map

Check of UnderstandingThe difference between true north and grid north

arises because . . .

Grid lines get closer together near the Earths poles

Latitude and longitude lines do not match grid lines

Lines of latitude are not parallel

Latitude and longitude lines match grid lines exactly

Check of UnderstandingWhich north changes position slightly

over time?

Grid North

Magnetic North

Geographic North

True North

Check of UnderstandingWhich of these symbols represents magnetic north?

Z

W

Y

X

Check of UnderstandingWhich of these statements about

the direction of magnetic north is true?

It is the same as grid north

It is the same as true north

It differs from both grid north and true north

It is the same as both true north and grid north

Check of UnderstandingCorrectly orientating your map will help you . . .

Find your location more easily

Read the contour numbers more easily

Read place names more easily

Measure distances more easily

Check of UnderstandingWhich of the following

is not a method for determining north without a compass?

Using shadows and a stick

Finding the wind direction

Using a watch and the sun

Finding the Pole Star

Check of UnderstandingFrom the diagram,

which letter indicates the correct position of the Pole Star?

Z

W

Y

X

Check of UnderstandingFrom the diagram,

if a shadow moves from position 1 to position 2which arrow points to the north?

Z

W

Y

X

Check of UnderstandingIf you hold your watch as in the diagram,

which arrow points to the north?

H

E

G

F

Leading Cadet Training

Basic Navigation

End of Presentation