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Interpreting Topographic MapsInterpreting Topographic Maps
Chapter 5
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Latitudes and Longitudes
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Coordinates
1. Geographical coordinates Latitudes: Imaginary horizontal lines
that run in an east-west direction
round the Earth.
e.g. 11051N
Longitudes: imaginary vertical lines
that run in a north-south direction
from the N
orth P
ole t
othe S
outh P
oleon the Earths surface.
e.g. 11051E
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Latitudes and Longitudes
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Latitudes and Longitudes
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0 Latitude: Equator
0 Longitude: Prime Meridian
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Latitudes and Longitudes
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Coordinates
Grid coordinates e.g. 2234, 321456
Eastings: vertical lines, numbered left to right.
(longitudes)
Northings: horizontal lines numbered bottom to
top. (Latitudes)
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How to read Grid Reference?
1. Identify the point or area
2. Identify the grid square where the point or areais found
3. Read the Eastings first (vertical lines)4. Read the Northing (horizontal lines)
5. Record down the grid reference
Always check to see which is the smaller gridnumber first.
Remember that E comes bef
ore N
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43
42
41
40
A
Easting
Northing
Grid Reference
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Grid Reference
4-figure grid reference or grid square
6 figure grid reference
The co-ordinates represent the whole square, not just the
single point.
30 31 32 34
43
42
41
40
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43
42
41
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A
4- figure grid reference
A = 3141
Grid Reference
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43
42
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A
6- figure grid reference
Grid Reference
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310 320
420
410
A
Grid Reference
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Grid Reference
310 320
420
410
A
6-figure grid reference
A = 313416
313
416
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30 31 32 33
43
42
41
40
A
6-figure grid reference
A = 313426
Grid Reference
416
313
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Compass Directions
Take note of where is
the reference point
and where is the point
of question.
Place the compass at
the reference point
and read the point ofquestion from the
reference point
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Bearings
Compass directions
Measured in degrees clockwise from north
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Compass Bearings
1. Connect a linebetween the twopoints, A and B.
2. Place your potractorat the Startinglocation (given inquestion) with 0oC
at North.
3. Read from North, ina clockwisedirection
A
B
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Compass Bearings
*Reminder: Read
from North,
clockwise direction.
180o + 62o = 242o
straight line = 180o
A
B
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Distance
1. Straight-line distance Using ruler
2. Curved distance Using string or paper
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Find the straight line distance
between A and B.
1. Connect point Aand B with astraight line.
2. Using a ruler,measure thedistance betweenpoint A and B.
3. Convert cm inmap to actualdistance in groundusing the scale
given.
A
B
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Find the curved-distance between A
and B.
Using a string,trace the distancefrom A to B.
Mark the ending
point on thestring.
Measure thelength recorded inthe string.
Convert the lengthon map into actualdistance onground using the
scale given.
AB
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Contours
a line that joins points of equal
elevation (height)
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ContourLines
Thenearerthe
linesaretogether,
thesteeperthe
slope (XY).
The furtherthe
linesareapart,the
gentlertheslope(AB).
100
150
200
250
50
YXBA
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Contours
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Contours
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