Transcript Basic Nav Pt 1

Basic Navigation
Leading Cadet Training
Basic Navigation
Map and Compass
Lecture
1
Basic Navigation
Basic navigation is –
Knowing where you are on the map.
Knowing where you want to get to.
And finding the best route to get there.
Good navigation is a combination of:
Good Map Reading Skills.
and good Compass Work.
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).
True, Magnetic & Grid North
True North is the direction to the earth's axis
Magnetic North is in Hudson Bay, Canada.
o
In the UK Grid North is about 2 East of True North.
The other problem is,
Magnetic North changes its position over time !
UK Grid North
Magnetic North
True North
True or Grid North ?
Lines of Longitude 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 match lines
of Latitude or Longitude,
nor do they point to the Magnetic pole,
or to the North Pole (True North)
Instead they are said to point to an
imaginary point called
Grid North
True or Grid North ?
So when navigating on a map we use
Grid North
Not Magnetic North
and not True North
The Symbol of
Magnetic North
The Symbol of
True North
The Symbol of
Grid North
Magnetic Variation
Magnetic Variation is the angular difference between
true north and magnetic north,
UK Grid North
and is different across the world.
In some areas it is east of true
Magnetic
north. North
True
North
So Magnetic Variation must always
be allowed for when using
a map and compass for navigating.
To help, magnetic variation is always
displayed on the bottom right of a Map.
Magnetic
Variation
Magnetic Variation
Because all compass references are made to either
Grid North or Magnetic North,
UK Grid North
the angular difference between
True
Magnetic
North
North
these 2 north's must be known.
This angular difference
is called the
Grid Magnetic Angle
(GMA)
Magnetic
Variation
Grid-Magnetic
Angle
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
to which a compass points,
and in the UK it is located approximately
1º West of Grid North.
Orientate Your Map
When using a map the first thing to do
is to Set the Map with your surroundings,
using identifiable features.
Hill
Woods
Island
Church
River
Orientate Your Map
Set the Map with your surroundings
Stream
junction
Shoulder on a
steep slope
You are
here
Old walled
enclosure
Re-entrant
at base of slope
Orientate Your Map
Set the GMA against the
direction of travel arrow
of your Compass.
If you
cannot
Put the compass
on the
map set the map
and align the North-South
using observable features
grid lines.
you can set it with your compass.
Turn map & compass
TOGETHER
until the needle falls
inside the orienting arrow –
red end pointing North.
Finding North
If 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
1. The Pole Star
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 times
their separation.
And there you find the Pole Star
Finding North
2. Using a Watch
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 and
the hour hand points South.
If you have a Digital watch,
draw a diagram showing the correct time,
and use that instead.
Due South.
Finding North
3. The Shadow Method
Place a stick in the ground
and mark the end of its shadow.
Wait for 10 to 15 minutes,
and then mark the new shadow.
A line between the marks
runs roughly west to east.
The line dissecting this
shows north to south
East
South
North
West
Check of Understanding
The difference between true north and grid north
arises because . . .
Latitude and longitude lines
do not match grid lines
Grid lines get closer together
near the Earths poles
Latitude and longitude lines
match grid lines exactly
Lines of latitude are not parallel
Check of Understanding
The position of the magnetic north pole:
Is not fixed but changes
a little every year
Is the same as
the true north pole
Is fixed and remains
in the same place constantly
Only changes when
new maps are issued
Check of Understanding
The angular difference between magnetic north
and grid north on a map is known as?
Compass deviation angle
Grid magnetic angle
Magnetic deviation angle
Grid deviation angle
Check of Understanding
Which of these symbols represents magnetic north?
W
X
Y
Z
Check of Understanding
What is the approximate difference
between true north and grid north?
0 to 5 degrees
6 to 8 degrees
8 to 10 degrees
More than 10 degrees
Check of Understanding
Which of these statements about
the direction of magnetic north is true?
It is the same as true north
It is the same as both
true north and grid north
It differs from both
grid north and true north
It is the same as grid north
Check of Understanding
Where on a M726 OS map
is the Technical Information giving details of
magnetic variation located:
The bottom right side
At the very top
On the extreme left
On the back
Check of Understanding
Which north do you use when navigation
with an Ordnance Survey map?
Grid North
True North
Geographic North
Magnetic North
Check of Understanding
When using a map what is the first thing you do?
Organise the Map
Sight the Map
Range the Map
Set the Map
Check of Understanding
Which of the following
is not a method for determining north
without a compass?
Finding the wind direction
Finding the Pole Star
Using a watch and the sun
Using shadows and a stick
Check of Understanding
From the diagram,
if a shadow moves from position 1 to position 2
which arrow points to the north?
W
X
Y
Z
Check of Understanding
How can you find north by day without a compass?
Use a map and stick
stuck vertically in the ground
Use your mobile phone
Ask the rest of the group
and make a considered decision
By pointing the hour hand
of your watch at the sun,
bisect the angle between that
and the 12 o'clock
Check of Understanding
From the diagram,
which letter indicates the correct position
of the Pole Star?
W
X
Y
Z
Basic Navigation
Leading Cadet Training
End of Presentation