Post on 06-Jul-2018
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Map Reading
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A Map is a birds eye view of thesurrounding area to help guide us
from one place to another.
What is a Map?
A traveller needs a map to help
them find their way aroundmore easily.
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Lines of Longitude
Lines of Longitude run parallel to the Prime
Meridian at Greenwich.
A line of
Longitude is
also referred toas a Meridian
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Lines of Latitude
• Lines of Latitude run parallel to the Equator
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Recording your Position
Lines of Latitude &Longitude cometogether to form amatrix
1.5
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Recording your Position
l 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
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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.
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Topographical Maps
This means they show the shape and surface
detail of the land. This includes natural and
man-made features.
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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.
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Folding your map
First fold your map in half length wise, with theprinted map outwards like so:
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Then concertinawise:
The unit of height used on this map is in
METRES.
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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 actuallydrawn on the map itself - it would be too
confusing.
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North
1. True North
2. Grid North
3. Magnetic north
In map reading there are always references to
north. There are in fact 3 north's:
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True North
This is the geographical north pole of the
earth - the point where the earth’s axis meet
the surface.
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Grid North
This north takes its name from the National GridSystem. This is a system of imaginary linesdrawn vertically & horizontally on the mapwhich 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 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.
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Magnetic North
This is the point the magnetic needle aligns
itself to when freely suspended. The earth hasits own magnetic field.
Unfortunately the earth’s north and southpoles do not line up with the geographical poles
- in fact they are about 1200 miles apart!!
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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.
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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 waybetween high and low tides.
By joining all the pointsat the same height you
can achieve a picture
and shape of the land.
50
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These contour lines will wonder all over the
map and will eventually rejoin at the startpoint to show an area of equal height.
The only exception to this rule is where acontour line meets a cliff face.
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The height is shown in small breaks in the
contour line.
Every 5th line is shown thicker to make themeasier to read.
These contour lines are situated at 10 metre
intervals.The rise & fall between contours is the Vertical
Interval (VI)
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Scales
The objective of this lecture is foryou to be able to display an
reasonable understanding of size and
scale in map work.
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IntroductionIf your map is to cover a reasonable area
then everything on the map has to be
reduced considerably from its real size.
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Why do we use scale?
We use scale so that we can cover a
reasonable area of the ground aroundus and show it on the map.
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How do you express scale?
There are 3 ways to express
scale.
These are:
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A: In Words
B 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.
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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 anydistances measured on the map are one-
fiftythousanth of the real distance on the
ground.
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A Representative Fraction is
also referred to as RF
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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
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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
l 1 inch on the map = 50,000 inches on the ground
l 1 cm on the map = 50,000 cm on the ground
l 1 m on the map = 50,000 m on the ground
So a 1:50,000 ratio would be equally validfor:
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If the scale is expressed in words it
may be necessary to convert it intoeither a RF or a ratio.
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For example: to convert a scale of 1 inch to
1 mile, you have to calculate the number ofinches 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)
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So the scale of 1 inch to 1 milecan 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 carefulthought.
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Area
When using scales, areas of ground
will also be proportionately reduced
but remember that areas contract
rapidly on small scale maps.
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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 thearea of a rectangular figure is length
multiplied by breadth. If you therefore halved
the scale you will quarter the area of themap.4
4
4 x 4 = 16
2
2
2 x 2 = 4
e.g.
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The same area of ground in three different scales
(Half the scale = One quarter of the area)
1 km square
at 1:12,500
1 km squareat 1:25,000
1 km square
at 1:50,000
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Examples of different scales:
Large scale - City or town maps(defined buildings)
Medium scale - Larger areas (buildings
as symbols)
Small scale - Atlas (large towns inname only)