# Basic Map Reading.ppt - Map Read by pengxuebo

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```									  Map Reading

1st Class Training Course
Introduction
• This lecture is a condensed version of the
Map Reading Training course. During this
lecture, you will learn about Maps and
their language and Scale.
• In part 2 of this lecture you will study Grid
References, Relief and Gradients & Inter-
visibility.
Agenda
•   What is a Map
•   Map Language
•   Scales
•   Grids
•   Relief
•   Gradients and Intervisibility
What is a Map?
• A Map is a birds eye view of
the surrounding area to help
guide us from one place to
another.

• A traveller needs a map to help them find
their way around more easily.
Lines of Longitude

A line of
Longitude is
also referred to
as a Meridian

• Lines of Longitude run parallel to the
Prime Meridian at Greenwich
Lines of Latitude

• Lines of Latitude run parallel to the Equator
• Lines of Latitude
& Longitude
come together to
form a matrix

1.5

   First we state its
Latitude followed
by its Longitude
in degrees &
minutes
e.g.: A= 20’N 56’W
B= 17’S 17’W
C= 45’N 15’E

1.5
• Although this system can give reasonably
accurate positioning it is not accurate
enough for everyday use.

• So each degree is further broken down
into 60 minutes.
Topographical Maps
The M726 series are classed as
topographical maps. This means they
show the shape and surface detail of the
land. This includes natural and man-
Get the latest edition

OS maps are constantly being updated. It is
always advisable to have the most up-to-date
map available as some features will change.

1) Roads  will be built
2) Rivers could become dams
3) New Buildings could be built

Some features such as mountainous areas
may stay fairly constant
Looking after your map
Some maps are now produced laminated and
you can treat maps with a waterproof coating

 Always keep your map folded
 NEVER mark a map surface with ink
 If you do need to mark your map do so
lightly with a pencil
 Try to avoid getting it wet
 If you do get it wet allow it to dry naturally.
First fold your map in half length wise, with
the printed map outwards like so:
1.9
Then concertinawise:
Remember: The M726 series
is a 1:50,000 scale map

The unit of height
used on this map is
in METRES.
Latitude / Longitude
The lines of latitude are expressed in
degrees and minutes and are marked
along the right and left (east and west)
hand side of the map.
The lines of longitude are marked along
the top and bottom (north and south). The
lines of latitude and longitude are not
actually drawn on the map itself - it would
be too confusing.
North

In map reading there are always references
to north. There are in fact 3 north's:

a) True North
b) Grid North
c) Magnetic north
True North
This is the geographical north pole of the
earth - the point where the earth’s axis
meet the surface.
Grid North
This north takes its name from the National
Grid System. This is a system of imaginary
lines drawn vertically & horizontally on the
map which divide it into a series of squares.
 Because Grid lines are drawn on a flat map
and lines of latitude & longitude are curved
like the the earth's surface. The 2 systems
are different.
 This difference is shown on the map (key
position 10) as a difference between True &
Grid north.
Magnetic North

This is the point the magnetic needle aligns
itself to when freely suspended. The earth
has its own magnetic field.

Unfortunately the earth’s north and south
poles do not line up with the geographical
poles - in fact they are about 1200 miles
apart!!
Sometimes the same symbol is shown in
different colours to signify a difference

example:

Red National Trust symbols show the area is
open all year.

The same symbol in blue indicates it has a
restricted opening period.
Contour Lines
A contour line is a reddish brown line drawn
on the map joining all points of equal height
above mean sea level (MSL) Mean sea level
is a fixed height approximately half way
between high and low tides calculated at
Newlyn in Cornwall over many years.
By joining all the points
50             at the same height you
can achieve a picture
and shape of the land.
These contour lines will wonder all over the
map and will eventually rejoin at the start
point to show an area of equal height.

The only exception to this rule is where a
contour line meets a cliff face.
The height is shown in small breaks in the
contour line.
Every 5th line is shown thicker to make them
These contour lines are situated at 10 metre
intervals on the M726 series.
The rise & fall between contours is the Vertical
Interval (VI)
Agenda
•   What is a Map
•   Map Language
•   Scales
•   Grids
•   Relief
•   Gradients and Intervisibility
Scales
• The objective of this lecture is for you to
be able to display an reasonable
understanding of size and scale in map
work.
Introduction
• If your map is to cover a reasonable
area then everything on the map has to
be reduced considerably from its real
size.
Why do we use scale?

We use scale so that we can
cover a reasonable area of the
ground around us and show it
on the map.
How do you express scale?

There are 3 ways to express
scale.

These are:
A: In Words
 by saying “so many centimetres to the kilometre”

Example: a scale of “2cm to 1km” means
that for every 2 cm on the map you would
travel 1 km on the ground.
Measuring the distance from the Squadron
headquarters to the local Police Station as
12cm on this scale would be equal to 6km
on the ground
B: As a Representative Fraction
In this method the scale is expressed in the
form of a fraction.

e.g.      1
50,000
Using this method you are saying that any
distances measured on the map are one-
fiftythousanth of the real distance on the
ground.
A Representative Fraction is
also referred to as RF
C: As a Ratio

This is very similar to B, but is written as:

1:50,000

this means the same as:

1
50,000
Calculation

In the case of RF and ratio the expression of
distance, whether it’s inches, centimetres or
metres, is the measurement on the ground

So a 1:50,000 ratio would be equally valid
for:
 1 inch on the map = 50,000 inches on the ground
 1 cm on the map = 50,000 cm on the ground
 1 m on the map    = 50,000 m on the ground
If the scale is expressed in
words it may be necessary to
convert it into either a RF or a
ratio.
For example: to convert a scale of 1 inch to
1 mile, you have to calculate the number of
inches in a mile:

• There are 1,760 yards in a mile

• There are 5,280 feet in a mile (1760 x 3)

• There are 63,360 inches in a mile (5280 x
12)
So the scale of 1 inch to 1 mile
can be expressed as a ratio of
1:63,360.
This type of calculation is made
easier using the metric system,
but it will still require careful
thought.
Area
When using scales, areas of
ground will also be
proportionately reduced but
remember that areas contract
rapidly on small scale maps.
For example if you take a map that is half the
scale of another, then the area is reduced by
a quarter (not a half). This is because the
area of a rectangular figure is length
multiplied by breadth. If you therefore halved
the scale you will quarter the area of the
map.
4                 2
e.g.
2
4

4 x 4 = 16        2x2=4
1 km square
at 1:12,500

1 km square
at 1:25,000

1 km square
at 1:50,000

The same area of ground in three different scales
(Half the scale = one quarter of the area)
Examples of different scales:

 Large   scale    - city or town maps
(defined buildings)
 Medium    scale - Larger areas (buildings
as symbols)
 Small   scale    - atlas (large towns in
name only)

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