lecture leading cadet training basic navigation 1 map and compass
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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
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