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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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30 31 32 33

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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30 31 32 33

43

42

41

40

A

4- figure grid reference

A = 3141

Grid Reference

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30 31 32 33

43

42

41

40

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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