Chapter 1

Map Reading

What is a topographic map ?• Large-scale map representing selected aspects of the

earth’s surface• Shows both physical and human features

Components of a topographic map• Title• Grid lines• Names of places• Scale• Direction• Contours• Legend and symbols

Chapter 1: Map Reading

Chapter 1: Map Reading

Some basic components of a topographic map

Title

Place name

Grid lines

Scale

Contour Symbols

Grid lines• Eastings – vertical lines that run from west to east• Northings – horizontal lines that run from south to north• Grid lines are numbered to provide the coordinates of

specific features on a map

Grid reference• Set of digits formed using the grid values of eastings

and northings• Defines a location on a map• The more digits in a grid reference, the more precise

the location, e.g. a six-figure grid reference gives a more accurate location than a four-figure grid reference

Chapter 1: Map Reading

Four-figure grid reference• Identifies a specific grid square• First two digits = Value of the easting on the left of the

square• Second two digits = Value of the northing at the bottom

of the square

32

31

3065 66 67

X

Example:

The four-figure grid reference for Point X is 6530.

Chapter 1: Map Reading

Six-figure grid reference• Identifies a specific point in a grid square• How:

1. Determine the four-figure grid reference

2. Divide the space between the two eastings of the grid square into ten equal intervals

3. Count how many tenths the point is from the left to right – add this number after the first two digits of the four-figure grid reference

4. Repeat Step 2 for the northings of the grid square

5. Count how many tenths the point is from the bottom up – add this number to the end of the grid reference

Example:

The six-figure grid reference for Point X is 655305

X

32

31

3065 66 67

Chapter 1: Map Reading

Scale• Shows what a certain distance on the map represents

on the land in the real world• Three ways to indicate scale on a map:

1. Line scale

– E.g.

2. Word statement

– E.g. “1cm on the map equals 30km on the ground”

3. Representative fraction

– E.g. ‘1:50,000’ means that one unit on the map represents 50,000 units on the ground in the real world

40 2 km

Chapter 1: Map Reading

1. Place a strip of paper on the line between the two points

2. Mark the two points on the edge of the paper strip

3. Place the marked edge of the paper strip on the line scale

4. Read the distance between the two points

Reading the straight-line distance between two points

Chapter 1: Map Reading

1. Place one end of a string at one end of the path to be measured (point ‘C’)

2. Using the string, trace the curved path

3. Mark the end of the path on the string (point ‘D’)

4. Place the string on the line scale

5. Read the distance off the scale

Reading the length of a curved path

Chapter 1: Map Reading

Direction• Two ways to describe the direction of a place

1. Using compass points

– Cardinal points of the compass: north, south, east, west

– Intercardinal points: northeast, southeast, southwest, northwest

2. Using bearings

– Direction of a place is expressed as an angle (in degrees) clockwise from the base direction (0)

– Base direction could be grid north, magnetic north or true north

Chapter 1: Map Reading

Grid north• Direction of the vertical grid lines (called eastings) on a

map

Magnetic north• Direction of the magnetic

north pole

True north• Direction of the geographic

north pole

Chapter 1: Map Reading

Land elevation1. Contours

– Lines on the map joining places with the same height– The number on a contour line indicates the height that the line represents

2. Spot heights– Points on the map showing the heights of hills

100

200

998

Chapter 1: Map Reading

3. Benchmarks– Marked points of known elevation which serve as reference points from which the height of other places may be established

4. Trigonometrical stations– Points marked by metal discs mounted on stable foundations such as concrete pillars

– Usually located on top of mountains or hills

– May be used as benchmarks for measuring elevation

4.38

480

Chapter 1: Map Reading

Recognising relief features• The shape of contour lines and the spacing between

them show us the shape, height and slope of relief features

Chapter 1: Map Reading

A plateau A mountain Undulating relief

Chapter 1: Map Reading

A gentle slope A stepped slope A steep slope

River features• Topographic maps can give us some information on the

river features of an area1. River source

– Point where a river originates

2. River mouth

– Point where a river ends

3. River course

– Path followed by a river

– Perennial course flows throughout the year

– Indefinite or seasonal course flows only during certain seasons

4. Watershed

– Boundary between two drainage basins

Chapter 1: Map Reading

5. Drainage pattern

– Pattern formed by the rivers in a particular drainage basin

Chapter 1: Map Reading

Trellis patternDendritic pattern

Centripetal pattern Radial pattern

Cross-sections• Drawing cross-sections will help you identify relief

features• How:

1. Draw a line (XY) across the map where the cross-section is to be drawn.

Chapter 1: Map Reading

2. Place a strip of paper on the line XY. Moving from left to right, mark each point on the edge of the paper where XY meets a contour.

Chapter 1: Map Reading

3. On another piece of paper, draw the horizontal and vertical axes for the cross-section. The horizontal axis should be the length of XY. Choose a suitable scale for the vertical axis.

4. Place the marked edge of the paper strip (from Step 2) along the horizontal axis of the cross-section graph. For each mark on the paper strip, draw a vertical line up to the equivalent height and mark off with a dot.

Chapter 1: Map Reading

5. Join all the dots with a smooth curve to complete the cross-section of XY.

Gradient• Tells us how steep a slope is• To calculate gradient:

Vertical distanceVertical distanceGradient =Gradient =

Horizontal distanceHorizontal distance

• A gradient of 1:25 means that for every horizontal

distance of 25 units covered, you would ascend one unit

Chapter 1: Map Reading