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Map interpretation
Contents
• Part 1 - Introduction to maps
• Title
• Key (sometimes called legend or explanation)
• Scales
• Contours
• Part 2 – Map interpretation
• Contour patterns
Part 1 - Introduction to maps
• A map is a representation of all or part of the Earth
drawn on a flat surface at a specific scale.
• Maps use a variety of symbols and colours to represent
selected features of an area.
TYPES OF MAPS
• General purpose maps (reference maps, )
• show both natural and human-made features such as
coastlines, lakes, rivers, boundaries, settlements, roads,
rail lines, and others.
• Thematic maps, (special-purpose maps, )
illustrate the geographical distribution of a particular theme or
phenomenon. Landforms, aspects of climate, vegetation and
soil types, demographics, industry, manufacturing, and natural
resources are examples of common thematic maps.
• topographic maps.
• As the term suggests, these maps show the topography or
surface features of the landscape through the use of
contour lines.
N
Scale
Key
UK Annual Mean Wind Speed
N
UK Bedrock Geology
Title
North
Point
The upper left side map is
political map for Europe
but the lower right-side map
is showing physical appearance
of Europe continent
• all maps share common properties or map basics that provide
information to assist the reader in studying and interpreting
the maps. and they are called map elements as listed below.
 Map elements
• a title,
• scale,
• legend,
• date of publication,
• direction,
• information about the map projection. etc
Direction: Direction tells you which way to hold the map.
By convention, most maps are made with their top portion
directed at North. The North direction is generally indicated by
an arrow in the maps
Legend is a guide which lists symbols and colours used on a map
to represent different geographic features. Legend helps to identify
what symbols and colours represent
Scale: can be defined as the ratio of the distance between two
points on the map and the same two points on the Earth’s surface.
topographic maps.
 As the term suggests, these maps show the topography or
surface features of the landscape through the use of contour
lines.
 Contours are lines on a map that join places of equal
elevation above sea level.
 This three-dimensional effect allows for detailed study of
landscape and drainage features.
 Topographic maps are usually of a large scale and show
many of the features of general-purpose maps in considerable
detail.
A
B
1 km
Topographic profile
topographic profile is a diagram that shows the
change in elevation of the land surface along any
given line (an area “looked from the side”).
How to Make a Topographic Profile
This represents a very simple topographic map of a hill. The hill is steep on the left side (the
contour lines are very close together) and has a gentle slope on the right side. The numbers
represent the elevation of the contour lines. (*)
What would the hill look like if you were to slice it from left to right? (*)
1
0
0
Thus you have a topographic profile. This is what the hill would look like if you were to cut it
along the profile line and look at it from the side. (*)
300
500 feet
400 feet
300 feet
200 feet
100 feet
Normally, the Earth’s surface is not this blocky. In a topographic profile a line is drawn from these
points (red dots) producing a smooth transition. (*)
200
4
0
0
 Contour lines
•Contour An imaginary line on the ground surface joining the points
of equal elevation is known as contour.
•It facilitates depiction of the relief of terrain in a two-dimensional
plan or map.
•In other words, contour is a line in which the ground surface is
intersected by a level surface obtained by joining points of equal
elevation. This line on the map represents a contour and is called
contour line.
•Contouring is the science of representing the verticaldimension of
the terrain on a two-dimensional map.
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• Contour Map
• a map showing contour lines is known as Contour map.
• A contour map gives an idea of the altitudes of the surface
features as well as their relative positions in plan serves the
purpose of both, a planand a section.
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Basicelementsofcontourmaps:
 index Contour Line is a bolded Contour lines with elevation numbers
above the sea level
 Contour Interval (CI) – It is the vertical distance between any two
consecutive contours.
This interval depends upon
(i) the nature of the ground (i.e. whether flat or sleep).
(ii) the scale of the map
(iii) the purpose of the survey.
 Horizontal equivalent (he) Horizontal equivalent is the horizontal
distance between two consecutive contour lines measured tothe scale of
the map.
 Gradient - The steepness of a slope as measured in degrees,
percentage, or as a distance ratio (rise/run).
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 lines
The difference in
elevation between
the two index
contours (800 - 700)
is 100. We cross
five lines as we go
from the 700 line to
the 800 line (NOTE:
We count the lines
between the index
contours, then ADD
one. In this case,
we have 4 lines + 1
= 5). Therefore is
we divide the
elevation
difference
(100) by the
numberof lines (5)
we will get the
contour interval. In
this
case it is 20.
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100
1400
5
35
200
4400
10
30
10
30
20
0
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20
180
200
1400
5
+25
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General Features of Contour Lines
 Topographic Maps can show:
elevation:
 Contour lines connect
points of equal elevation.
Topographic Maps can show:
if the land is steep or gentle
 Steep slopes are shown
by closely spaced contour
lines.
 Gentle slopes are shown
by widely spaced contour
lines.
 Contour lines do not
intersect, branch or cross.
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 Topographic Maps can identify whether it is a ridge or a valley,
rivers and streams flow directions:
 Contour line cross ridge line at right angles. If the higher values are inside
the bend or loop in the contour, it indicates a ridge.
Rule 9 - Contour lines create V (or U) patterns when they cross a ridge. The tip or blunt end of the V or U at a ridge ALWAYS points
downhill.
Contour lines form V’s that point upstream when they cross a stream. ■ It is important to remember that they point in the opposite direction as the flow of water.
The spur is the higher lying ground adjacent to the valley. • Spurs are identified as follows: – The rounded “Ushaped” contours point towards lower ground. – Spurs will
not have rivers present
• A valley may be identified in the following manner: – The sharp “V-shaped” contours point towards higher ground. – A valley usually has some form of river or stream
present.
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8) Contour line cross ridge or valley line at right angles.
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If the higher values are outside the bend it represents a valley.
 When contour lines cross
streams they bend in upstream;
that means, the contour line
forms a 'V or U-shaped' with
the apex at the intersection
with the stream, and pointing
in an upstream direction.
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v) Contour line cross ridge or valley line atright angles.
If the higher values
are inside the bend or loop in the contour,
itindicates a Ridge.
Contour line cross ridge or valley line at right angles. If the higher values are inside the bend or
loop in the contour it indicates a ridge. 8) Contour line cross ridge or valley line at right angles.
If the higher values are outside the bend it represents a valley.
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70
60
50
RIDGE LINE
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RIDGE VALLEY
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index Contour Line : is a bolded Contour lines with elevation
numbers above the sea level
Contour Interval (CI) – It is the vertical distance between any
twoconsecutive contours.
This interval depends upon
(iv) the nature of the ground (i.e. whether flat or sleep).
(v) the scale of the map
(vi) the purpose of the survey.
 Horizontal equivalent (he) Horizontal equivalent is the
horizontal distance between two consecutive contour lines
measured tothe scale of the map.
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uniformly spaced.
iv) A plane surface when they are straight, parallel
andequally spaced.
CHARACTERISTICS OF CONTOURS
i) All points in a contour line have the same elevation.
ii) Flat ground is indicated where the contours are
widelyseparated and steep-slope where they run close
together.
iii) Auniform slope is indicated when the contour lines are
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examples
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CHARACTERISTICS OF CONTOURS
i) A series of closed
contour lines on the 80
map represent a hill 75
, if the higher values 70
are inside 65
60
HILL
60
65
70
75
80
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CHARACTERISTICS OF CONTOURS
80
vii) A
series of 75
closed contour 70
lines on the map 65
indicate a
depression if the 60
higher values
areoutside
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60
65
70
75
80
A DEPRESSION
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CHARACTERISTICS OF CONTOURS
viii) Contour line cross ridge or valley line at
right angles. If the higher values
100
90
80
are inside the bend orloop in the contour, itindicates a
Ridge.
70
60
50
RIDGE LINE
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CHARACTERISTICS OF CONTOURS
vii) Contour line cross ridge or valley line at
right angles.
If the higher values are
outside the bend, it
100 represents aValley
90
80
70
60
50
VALLEY LINE
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CHARACTERISTICS OF CONTOURS
viii). Contours cannot end anywhere but close
on themselves either within or outside the
limits
of the map.
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CHARACTERISTICS OF CONTOURS
ix).
Contour lines cannot 40
merge or cross one 30
another on map 20
exceptin the case of
an overhanging cliff.
40 30 20 10
OVERHANGING CLIFF
10
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CHARACTERISTICS OF CONTOURS
x)Contour lines never run
into one another except
in the case of vertical cliff.
In this case, several Contours
coincide and the horizontal
equivalent becomes zero.
OVERHANGING CLIFF
VERTIC
CLIFF
10 20 30 40
50
30
50
40
20
10
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CHARACTERISTICS OF CONTOURS
XI) Depressions between
summits is called a saddle.
Itis represented by four sets
of contours as shown. It
represents a dip in a ridge
or
the junction of two ridges. 70
And in the case of a mountain
80 range, i t takes the form of
a 90
pass.
SADDLE 70
80
90
90
100
110
Line passing through the saddles and summits gives watershed line.
23
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200
150
100
50
Think where is the steepest slope on this island?
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Steepest slope –
contour lines are
closest together
Sparrow
point 227
.76
150
200
100
50
Sometimes spot heights can be shown as a dot with a noteof the
height of that particular place.
A trigonometrical point (or trig point) shows the highest point in
an area (in meters and is shown as a blue triangle
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the shape and pattern of the contour lines
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PURPOSE (uses) OF CONTOURING/CONTOUR MAP
Contour survey is carried out at the starting of any
engineering project such as a road, a railway, a canal,
adam, a building etc.
i) contour maps are prepared in order to select the
mosteconomical or suitable site.
ii) It helps to locate the alignment of a canal so that itshould follow a ridge line.
iii) It helps to mark the alignment of roads and railways so
that the quantity of earthwork both in cutting and
fillingshould be minimum.
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iv) It helps for getting information about the groundwhether it is flat, undulating or mountainous.
v) It helps to find the capacity of a reservoir and
volumeof earthwork especially in a mountainous
region.
vi) It helps to trace out the given grade of a particularroute.
vii) It helps to locate the physical features of the
groundsuch as a pond depression, hill, steep or small
slopes.
(Undulating – rising & falling
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The scale bar shows a measurement on the map and
the specific distance it represents on the ground
© Crown Copyright/database right 2014. An Ordnance Survey/EDINA supplied service.
1 km
N
Cowers Lane to Shottlegate
is about 1 km
N
200 km
alway to Dublin
about 200 km
G
is
Presenter
2017-11-28 13:52:04
--------------------------------------------
Stress that scale bars are useful when
m
a
p
s
a
r
e
being enlarged or reduced, because
they maintain their proportion and can
still be used (show reduced inset map
as an example)
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Contours
• Contours are lines joining points of equal value.
This value on topographic maps is height (or
elevation/altitude) above mean sea level (MSL)
• Each successive contour represents an increase or
decrease in constant value. Often every 5th
contour
will be in bold to help identification
• Contours are normally associated with changes in
height, but they can represent any parameter
(e.g. thickness, pressure, rainfall). They can also
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be called iso-lines (e.g. isopachs, isobars, isohyets)
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Contours show the distribution and relative
size of any measured value
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Surface air pressure is measured in millibars
and is shown here as isobars
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Contours can show the distribution and
relative size of any measured value
This map shows the thickness
of the Earth’s crust (in kms)
This map shows rainfall
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data for Australia (in mm)
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Let’s return to topographic maps - on the map the land
surface looks flat, but the contours indicate otherwise
X
View from Point X towards the
SW, showing a valley and
a hill in the distance
N
© Crown Copyright/database right 2014. An Ordnance Survey/EDINA supplied service.
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1 km
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Contours never cross and will at some point close, although
this may be off the map. Topographic contours that close
in concentric patterns delineate hills or depressions
1 km
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1 km
Contours are drawn perpendicular to the maximum slope,
with the spacing between contours indicating
the steepness of the slope
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Valley and
stream
Ridge
Based on the shape of contours, landforms such
as valleys and ridges can be recognised
1 km
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This image highlights the real shape of two hills
and how they are shown on a contour map
40m
30m
20m
10m
0 MSL
Image from OS Map reading made easy.
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https://www.ordnancesurvey.co.uk/resources/map-reading/index.html
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You can watch a video explaining how to read
contour lines on an Ordnance Survey map
Click here to play…
The Ordnance Survey website has further information on
all aspects of maps and map reading, including how to
work out grid references and take compass bearings
https://www.ordnancesurvey.co.uk/resources/map-reading/index.html
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Practical exercise 1
Drawing contours
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900m 920m 900m
835m
835m
880m
900m
700m 1070m
800m 900m
800m
800m
1100m
970m
950m
875m
975m
Presenter
2017-11-28 13:52:05
--------------------------------------------
Sometimes topographic maps are
shown w
i
t
hheight values at a given point,
rather than contours. These are called
‘spot height’ maps and they are rather
difficult to interpret. In order to get a
better idea of the shape of the land
surface the data can be contoured.
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The easiest way to draw a contour map based on spot heights is to simply
interpolate between the known values.
As you interpolate between points make sure you label the new values,
as it quickly becomes very confusing if you don’t!
Then join identical values with smooth curves to create contours that
simulate topography
800m 800m
Start by interpolating
between individual
points, labelling new
values as you go.
750m 750m
700m
750m 800m
Then join up all
the original and
interpolated points
of equal value to
form contours.
800m
850m
750m
700m
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900m
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900m 920m
875m
900m
800m 800m
700m
800m
1100m
970m
950m
900m
1070m
900m
880m
835m
835m
975m
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Completing the contouring exercise
• Based on the contour map you have created:
• Where is the highest ground?
• Where is the lowest area?
• Describe the major landforms
• Mark on the most likely course of a stream and
determine in which direction it is flowing
Presenter
2017-11-28 13:52:06
--------------------------------------------
The highest ground is in the north (
>
1
1
0
0
m
)
.
The lowest area is in the SW, in the valley b
o
t
t
o
m(<700m).
The major landforms are a sinuous valley t
h
a
ttrends SW-NE,
then W-E, flanked by a broad ridge that trends NW-SE.
The ground rises from the valley bottom to a high point in
the north. The stream is flowing from east to west.
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970m
1100m
975m
900m
800m
950
900
850
920m
800m
875m
835m
900m
880m
950m
900m
700m 1070m
835m
Presenter
2017-11-28 13:52:07
--------------------------------------------
The highest ground is in the north (
>
1
1
0
0
m
)
.
The lowest area is in the SW, in the valley b
o
t
t
o
m
(<700m).
The major landforms are a sinuous valley t
h
a
ttrends
SW-NE, then W-E, flanked by a broad ridge that
trends NW-SE. The ground rises from the valley
bottom to a high point in the north. The stream is
flowing from east to west.
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800m
900m
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Part 2 – Map interpretation
• Contour patterns can be used to recognise
distinctive landforms such as ridges,
valleys and hills
• Contours may appear as black or coloured lines
on maps, and are often supported by colour
shading to give an impression of relief
• Cross-sections provide a useful way of visualizing
the shape of the land surface, but care needs to be
taken in their construction, particularly in terms of
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vertical exaggeration
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Previously we looked at the topography in this area
– let’s take a closer look at the contours
N
1 km
© Crown Copyright/database right 2014. An Ordnance Survey/EDINA supplied service.
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150m contour
The contour interval is 10m
with bold lines every 50m
N
© Crown Copyright/database right 2014. An Ordnance Survey/EDINA supplied service.
What is the contour interval?
1 km
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Locate the 150m contour between Shottle and Blackbrook
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N
© Crown Copyright/database right 2014. An Ordnance Survey/EDINA supplied service.
If you walked along this contour, what would your route be like?
150m contour
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Flat, as long as you remain on the 150m contour
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Downhill
100m contour
150m contour
N
© Crown Copyright/database right 2014. An Ordnance Survey/EDINA supplied service.
Which direction is downhill from the 150m contour?
200m contour
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N
© Crown Copyright/database right 2014. An Ordnance Survey/EDINA supplied service.
What else about the contours help to determine the direction
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of slope? The contour values are perpendicular to the slope,
with the bottom of the number on the downhill side
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A B
N
© Crown Copyright/database right 2014. An Ordnance Survey/EDINA supplied service.
What does the hillside look like if you stand at Point A
1 km
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and look towards Point B? It would go downhill to
the stream and then uphill again to Point B
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A useful technique to visualise landforms is to
draw a cross-section. This one is between
Points A and B on the previous map
No vertical exaggeration
A B
200
100
Valley with stream
0 100 200 300 400 500 600 700 800 900
Distance (metres)
This image shows a similar
valley in the area, confirming
the gentle slope angles
Contour
value
(metres)
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The X axis represents distance and the Y axis height
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When drawing cross-sections it is important to
be aware how the scales affect your
perception of slope angle
2x vertical exaggeration
A B
200 Valley with stream
100
0 100 200 300 400 500 600 700 800
Distance (metres)
The purpose will dictate the
scales you use. If the cross-
section is to highlight relative
changes in topography then a
vertical exaggeration is fine,
despite the fact that it increases
the angles of all sloping lines
If there is a need to add sub-
surface geology or calculate true
slope angles, then there should
be no vertical exaggeration
Contour
value
(metres)
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Compare the effects of vertical exaggeration
on the same cross-section
Notice how the change in
vertical exaggeration
affects the angles of slope
Bear this in mind when
drawing your own cross-
sections and decide how
much (if any) vertical
exaggeration is required
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N
© Crown Copyright/database right 2014. An Ordnance Survey/EDINA supplied service.
You now know how to identify a sloping valley by the shape of
Uphill
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the contours. They form a V-shape that points uphill
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Arrows indicate downhill
direction of valleys
N
© Crown Copyright/database right 2014. An Ordnance Survey/EDINA supplied service.
There are lots of valleys on the map; mark them with an arrow
Presenter
2017-11-28 13:52:09
--------------------------------------------
This map shows some of the main
valleys (
n
o
tall have been marked)
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pointing in the downhill direction
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Arrows indicate downhill
direction of valleys
N
© Crown Copyright/database right 2014. An Ordnance Survey/EDINA supplied service.
Notice that all the rivers are in valleys, but not all the valleys
Presenter
2017-11-28 13:52:09
--------------------------------------------
There is no permanent water in these
v
a
l
l
e
y
s
,however in the past there was
sufficient water that flowed along these
routes to cause erosion and form the
valley. Is there any time in the recent
geological past when there was greater
water flow in this area?
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have a river. Why is this the case?
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N
© Crown Copyright/database right 2014. An Ordnance Survey/EDINA supplied service.
What feature do the contours in the red area represent?
Presenter
2017-11-28 13:52:09
--------------------------------------------
Notice that the contours have a
similars
h
a
p
e
t
oa valley, but the V-shape
points downhill
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A broad, N-S trending ridge
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We can draw a cross-section
to confirm our idea
C
D
N
© Crown Copyright/database right 2014. An Ordnance Survey/EDINA supplied service.
It may help if you imagine you are standing at Point C on the 150m
Axis of ridge
Presenter
2017-11-28 13:52:09
--------------------------------------------
Answer: No; Point D is at the same
height (
1
5
0
m
)as Point C, but the axis of the
ridge is higher (at 175m).
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contour, looking towards Point D. Would you be able to see Point D?
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Cross-section showing the broad, gentle ridge
between Points C and D
2x vertical exaggeration
200
100
C D
Ridge
Standing at Point C you
would be unable to see
Point D because the
crest of the ridge is
higher than Point D
Here some vertical
exaggeration is
appropriate because
0 100 200 300 400 500 600
Distance (metres)
the relief is very subtle
Contour
value
(metres)
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Practical exercise 2
Constructing cross-sections
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Before constructing a cross-
section, look at the contours
and try to imagine what the
surface topography looks like
Narrower range of contours
between 140-160m indicate
a relatively flat hill top
Widely spaced contours
showing less steep slopes
compared to those in the east
Closely spaced
contours showing
a steep slope
A A’
We will now draw our own cross-
section between Cowers Lane (A)
and Chevinside (A’)
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Label each contour height and
plot the value directly onto the
Y-axis of the cross-section
A
200m
A’
150m
100m
50m
Use graph paper to mark on
every time a contour crosses
the chosen line of section
110
105
100
95
90
85
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This surface should be drawn free
hand to give a natural shape that
honours the contours
A
200m
A’
150m
100m
50m 4x vertical exaggeration
Once all the contour heights along
the section have been plotted the
land surface can be added
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A A’
4x vertical exaggeration
East
West
A completed cross-section between A-A’
The vertical scale has been exaggerated in order to show
the subtle relief. To calculate the vertical exaggeration,
divide the horizontal scale (1cm to 200m) by the
vertical scale (1cm to 50m)
So, 200/50 = 4x vertical exaggeration
200m
150m
100m
50m
0
1 km 2 km 3 km
Prepared by Eng Shuaib [Type here]
Scale 1: 20 000
Prepared by Eng Shuaib [Type here]
Comparison between a vertically exaggerated
section and a true scale cross-section
200m
150m
100m
50m
0
200m
0
No vertical exaggeration
4x vertical exaggeration
Prepared by Eng Shuaib [Type here]
The vertically exaggerated section provides a clearer representation
of subtle landforms, the other a true representation of slope angles
Prepared by Eng Shuaib [Type here]
Learning outcomes
You have now been introduced to the basic elements
of topographic maps
You have used contours to identify common landforms
and begun to visualise them in 3-D
You can now construct cross-sections and understand
the concept of vertical exaggeration
Prepared by Eng Shuaib [Type here]
Handouts required for the practicals
Slide 50: print out at A4, in B/W, portrait format
Slide 51: print out at A4, in colour, portrait format
Slide 52: print out at A4, in colour, portrait format
Graph paper for constructing the cross-section
Prepared by Eng Shuaib [Type here]
975m
900m
920m
900m
835m
835m
880m
900m
700m 1070m
800m 900m
800m
800m
1100m
970m
950m
875m
Prepared by Eng Shuaib [Type here]
N
© Crown Copyright/database right 2014. An Ordnance Survey/EDINA supplied service.
1 km
Prepared by Eng Shuaib [Type here]
A A’
Prepared by Eng Shuaib [Type here]

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Maps-and-map-interpretation.docx

  • 1. Map interpretation Contents • Part 1 - Introduction to maps • Title • Key (sometimes called legend or explanation) • Scales • Contours • Part 2 – Map interpretation • Contour patterns
  • 2. Part 1 - Introduction to maps • A map is a representation of all or part of the Earth drawn on a flat surface at a specific scale. • Maps use a variety of symbols and colours to represent selected features of an area.
  • 3. TYPES OF MAPS • General purpose maps (reference maps, ) • show both natural and human-made features such as coastlines, lakes, rivers, boundaries, settlements, roads, rail lines, and others. • Thematic maps, (special-purpose maps, ) illustrate the geographical distribution of a particular theme or phenomenon. Landforms, aspects of climate, vegetation and soil types, demographics, industry, manufacturing, and natural resources are examples of common thematic maps. • topographic maps. • As the term suggests, these maps show the topography or surface features of the landscape through the use of contour lines.
  • 4. N Scale Key UK Annual Mean Wind Speed N UK Bedrock Geology Title North Point
  • 5. The upper left side map is political map for Europe but the lower right-side map is showing physical appearance of Europe continent
  • 6. • all maps share common properties or map basics that provide information to assist the reader in studying and interpreting the maps. and they are called map elements as listed below.  Map elements • a title, • scale, • legend, • date of publication, • direction, • information about the map projection. etc
  • 7. Direction: Direction tells you which way to hold the map. By convention, most maps are made with their top portion directed at North. The North direction is generally indicated by an arrow in the maps Legend is a guide which lists symbols and colours used on a map to represent different geographic features. Legend helps to identify what symbols and colours represent Scale: can be defined as the ratio of the distance between two points on the map and the same two points on the Earth’s surface.
  • 8.
  • 9. topographic maps.  As the term suggests, these maps show the topography or surface features of the landscape through the use of contour lines.  Contours are lines on a map that join places of equal elevation above sea level.  This three-dimensional effect allows for detailed study of landscape and drainage features.  Topographic maps are usually of a large scale and show many of the features of general-purpose maps in considerable detail.
  • 10. A B
  • 11. 1 km Topographic profile topographic profile is a diagram that shows the change in elevation of the land surface along any given line (an area “looked from the side”).
  • 12. How to Make a Topographic Profile This represents a very simple topographic map of a hill. The hill is steep on the left side (the contour lines are very close together) and has a gentle slope on the right side. The numbers represent the elevation of the contour lines. (*) What would the hill look like if you were to slice it from left to right? (*)
  • 13. 1 0 0 Thus you have a topographic profile. This is what the hill would look like if you were to cut it along the profile line and look at it from the side. (*) 300 500 feet 400 feet 300 feet 200 feet 100 feet Normally, the Earth’s surface is not this blocky. In a topographic profile a line is drawn from these points (red dots) producing a smooth transition. (*) 200 4 0 0
  • 14.  Contour lines •Contour An imaginary line on the ground surface joining the points of equal elevation is known as contour. •It facilitates depiction of the relief of terrain in a two-dimensional plan or map. •In other words, contour is a line in which the ground surface is intersected by a level surface obtained by joining points of equal elevation. This line on the map represents a contour and is called contour line. •Contouring is the science of representing the verticaldimension of the terrain on a two-dimensional map.
  • 15. Prepared by Eng Shuaib [Type here]
  • 16. Prepared by Eng Shuaib [Type here] • Contour Map • a map showing contour lines is known as Contour map. • A contour map gives an idea of the altitudes of the surface features as well as their relative positions in plan serves the purpose of both, a planand a section.
  • 17. Prepared by Eng Shuaib [Type here] Basicelementsofcontourmaps:  index Contour Line is a bolded Contour lines with elevation numbers above the sea level  Contour Interval (CI) – It is the vertical distance between any two consecutive contours. This interval depends upon (i) the nature of the ground (i.e. whether flat or sleep). (ii) the scale of the map (iii) the purpose of the survey.  Horizontal equivalent (he) Horizontal equivalent is the horizontal distance between two consecutive contour lines measured tothe scale of the map.  Gradient - The steepness of a slope as measured in degrees, percentage, or as a distance ratio (rise/run).
  • 18. Prepared by Eng Shuaib [Type here]  lines The difference in elevation between the two index contours (800 - 700) is 100. We cross five lines as we go from the 700 line to the 800 line (NOTE: We count the lines between the index contours, then ADD one. In this case, we have 4 lines + 1 = 5). Therefore is we divide the elevation difference (100) by the numberof lines (5) we will get the contour interval. In this case it is 20.
  • 19. Prepared by Eng Shuaib [Type here] 100 1400 5 35 200 4400 10 30 10 30 20 0
  • 20. Prepared by Eng Shuaib [Type here] 20 180 200 1400 5 +25
  • 21. Prepared by Eng Shuaib [Type here] General Features of Contour Lines  Topographic Maps can show: elevation:  Contour lines connect points of equal elevation. Topographic Maps can show: if the land is steep or gentle  Steep slopes are shown by closely spaced contour lines.  Gentle slopes are shown by widely spaced contour lines.  Contour lines do not intersect, branch or cross.
  • 22. Prepared by Eng Shuaib [Type here]  Topographic Maps can identify whether it is a ridge or a valley, rivers and streams flow directions:  Contour line cross ridge line at right angles. If the higher values are inside the bend or loop in the contour, it indicates a ridge. Rule 9 - Contour lines create V (or U) patterns when they cross a ridge. The tip or blunt end of the V or U at a ridge ALWAYS points downhill. Contour lines form V’s that point upstream when they cross a stream. ■ It is important to remember that they point in the opposite direction as the flow of water. The spur is the higher lying ground adjacent to the valley. • Spurs are identified as follows: – The rounded “Ushaped” contours point towards lower ground. – Spurs will not have rivers present • A valley may be identified in the following manner: – The sharp “V-shaped” contours point towards higher ground. – A valley usually has some form of river or stream present.
  • 23. Prepared by Eng Shuaib [Type here] 8) Contour line cross ridge or valley line at right angles.
  • 24. Prepared by Eng Shuaib [Type here] If the higher values are outside the bend it represents a valley.  When contour lines cross streams they bend in upstream; that means, the contour line forms a 'V or U-shaped' with the apex at the intersection with the stream, and pointing in an upstream direction.
  • 25. Prepared by Eng Shuaib [Type here] v) Contour line cross ridge or valley line atright angles. If the higher values are inside the bend or loop in the contour, itindicates a Ridge. Contour line cross ridge or valley line at right angles. If the higher values are inside the bend or loop in the contour it indicates a ridge. 8) Contour line cross ridge or valley line at right angles. If the higher values are outside the bend it represents a valley.
  • 26. Prepared by Eng Shuaib [Type here] 70 60 50 RIDGE LINE
  • 27. Prepared by Eng Shuaib [Type here]
  • 28. Prepared by Eng Shuaib [Type here] RIDGE VALLEY
  • 29. Prepared by Eng Shuaib [Type here]
  • 30. Prepared by Eng Shuaib [Type here]
  • 31. Prepared by Eng Shuaib [Type here] index Contour Line : is a bolded Contour lines with elevation numbers above the sea level Contour Interval (CI) – It is the vertical distance between any twoconsecutive contours. This interval depends upon (iv) the nature of the ground (i.e. whether flat or sleep). (v) the scale of the map (vi) the purpose of the survey.  Horizontal equivalent (he) Horizontal equivalent is the horizontal distance between two consecutive contour lines measured tothe scale of the map.
  • 32. Prepared by Eng Shuaib [Type here]
  • 33. Prepared by Eng Shuaib [Type here] uniformly spaced. iv) A plane surface when they are straight, parallel andequally spaced. CHARACTERISTICS OF CONTOURS i) All points in a contour line have the same elevation. ii) Flat ground is indicated where the contours are widelyseparated and steep-slope where they run close together. iii) Auniform slope is indicated when the contour lines are
  • 34. Prepared by Eng Shuaib [Type here] examples
  • 35. Prepared by Eng Shuaib [Type here]
  • 36. Prepared by Eng Shuaib [Type here] CHARACTERISTICS OF CONTOURS i) A series of closed contour lines on the 80 map represent a hill 75 , if the higher values 70 are inside 65 60 HILL 60 65 70 75 80
  • 37. Prepared by Eng Shuaib [Type here] CHARACTERISTICS OF CONTOURS 80 vii) A series of 75 closed contour 70 lines on the map 65 indicate a depression if the 60 higher values areoutside
  • 38. Prepared by Eng Shuaib [Type here] 60 65 70 75 80 A DEPRESSION
  • 39. Prepared by Eng Shuaib [Type here] CHARACTERISTICS OF CONTOURS viii) Contour line cross ridge or valley line at right angles. If the higher values 100 90 80 are inside the bend orloop in the contour, itindicates a Ridge. 70 60 50 RIDGE LINE
  • 40. Prepared by Eng Shuaib [Type here] CHARACTERISTICS OF CONTOURS vii) Contour line cross ridge or valley line at right angles. If the higher values are outside the bend, it 100 represents aValley 90 80 70 60 50 VALLEY LINE
  • 41. Prepared by Eng Shuaib [Type here] CHARACTERISTICS OF CONTOURS viii). Contours cannot end anywhere but close on themselves either within or outside the limits of the map.
  • 42. Prepared by Eng Shuaib [Type here] CHARACTERISTICS OF CONTOURS ix). Contour lines cannot 40 merge or cross one 30 another on map 20 exceptin the case of an overhanging cliff. 40 30 20 10 OVERHANGING CLIFF 10
  • 43. Prepared by Eng Shuaib [Type here] CHARACTERISTICS OF CONTOURS x)Contour lines never run into one another except in the case of vertical cliff. In this case, several Contours coincide and the horizontal equivalent becomes zero. OVERHANGING CLIFF VERTIC CLIFF 10 20 30 40 50 30 50 40 20 10
  • 44. Prepared by Eng Shuaib [Type here] CHARACTERISTICS OF CONTOURS XI) Depressions between summits is called a saddle. Itis represented by four sets of contours as shown. It represents a dip in a ridge or the junction of two ridges. 70 And in the case of a mountain 80 range, i t takes the form of a 90 pass. SADDLE 70 80 90 90 100 110 Line passing through the saddles and summits gives watershed line. 23
  • 45. Prepared by Eng Shuaib [Type here] 200 150 100 50 Think where is the steepest slope on this island?
  • 46. Prepared by Eng Shuaib [Type here] Steepest slope – contour lines are closest together Sparrow point 227 .76 150 200 100 50 Sometimes spot heights can be shown as a dot with a noteof the height of that particular place. A trigonometrical point (or trig point) shows the highest point in an area (in meters and is shown as a blue triangle
  • 47. Prepared by Eng Shuaib [Type here] the shape and pattern of the contour lines
  • 48. Prepared by Eng Shuaib [Type here]
  • 49. Prepared by Eng Shuaib [Type here]
  • 50. Prepared by Eng Shuaib [Type here]
  • 51. Prepared by Eng Shuaib [Type here]
  • 52. Prepared by Eng Shuaib [Type here] PURPOSE (uses) OF CONTOURING/CONTOUR MAP Contour survey is carried out at the starting of any engineering project such as a road, a railway, a canal, adam, a building etc. i) contour maps are prepared in order to select the mosteconomical or suitable site. ii) It helps to locate the alignment of a canal so that itshould follow a ridge line. iii) It helps to mark the alignment of roads and railways so that the quantity of earthwork both in cutting and fillingshould be minimum.
  • 53. Prepared by Eng Shuaib [Type here] iv) It helps for getting information about the groundwhether it is flat, undulating or mountainous. v) It helps to find the capacity of a reservoir and volumeof earthwork especially in a mountainous region. vi) It helps to trace out the given grade of a particularroute. vii) It helps to locate the physical features of the groundsuch as a pond depression, hill, steep or small slopes. (Undulating – rising & falling
  • 54. Prepared by Eng Shuaib [Type here]
  • 55. Prepared by Eng Shuaib [Type here]
  • 56. Prepared by Eng Shuaib [Type here] The scale bar shows a measurement on the map and the specific distance it represents on the ground © Crown Copyright/database right 2014. An Ordnance Survey/EDINA supplied service. 1 km N Cowers Lane to Shottlegate is about 1 km N 200 km alway to Dublin about 200 km G is Presenter 2017-11-28 13:52:04 -------------------------------------------- Stress that scale bars are useful when m a p s a r e being enlarged or reduced, because they maintain their proportion and can still be used (show reduced inset map as an example)
  • 57. Prepared by Eng Shuaib [Type here] Contours • Contours are lines joining points of equal value. This value on topographic maps is height (or elevation/altitude) above mean sea level (MSL) • Each successive contour represents an increase or decrease in constant value. Often every 5th contour will be in bold to help identification • Contours are normally associated with changes in height, but they can represent any parameter (e.g. thickness, pressure, rainfall). They can also
  • 58. Prepared by Eng Shuaib [Type here] be called iso-lines (e.g. isopachs, isobars, isohyets)
  • 59. Prepared by Eng Shuaib [Type here] Contours show the distribution and relative size of any measured value
  • 60. Prepared by Eng Shuaib [Type here] Surface air pressure is measured in millibars and is shown here as isobars
  • 61. Prepared by Eng Shuaib [Type here] Contours can show the distribution and relative size of any measured value This map shows the thickness of the Earth’s crust (in kms) This map shows rainfall
  • 62. Prepared by Eng Shuaib [Type here] data for Australia (in mm)
  • 63. Prepared by Eng Shuaib [Type here] Let’s return to topographic maps - on the map the land surface looks flat, but the contours indicate otherwise X View from Point X towards the SW, showing a valley and a hill in the distance N © Crown Copyright/database right 2014. An Ordnance Survey/EDINA supplied service.
  • 64. Prepared by Eng Shuaib [Type here] 1 km
  • 65. Prepared by Eng Shuaib [Type here] Contours never cross and will at some point close, although this may be off the map. Topographic contours that close in concentric patterns delineate hills or depressions 1 km
  • 66. Prepared by Eng Shuaib [Type here] 1 km Contours are drawn perpendicular to the maximum slope, with the spacing between contours indicating the steepness of the slope
  • 67. Prepared by Eng Shuaib [Type here] Valley and stream Ridge Based on the shape of contours, landforms such as valleys and ridges can be recognised 1 km
  • 68. Prepared by Eng Shuaib [Type here] This image highlights the real shape of two hills and how they are shown on a contour map 40m 30m 20m 10m 0 MSL Image from OS Map reading made easy.
  • 69. Prepared by Eng Shuaib [Type here] https://www.ordnancesurvey.co.uk/resources/map-reading/index.html
  • 70. Prepared by Eng Shuaib [Type here] You can watch a video explaining how to read contour lines on an Ordnance Survey map Click here to play… The Ordnance Survey website has further information on all aspects of maps and map reading, including how to work out grid references and take compass bearings https://www.ordnancesurvey.co.uk/resources/map-reading/index.html
  • 71. Prepared by Eng Shuaib [Type here] Practical exercise 1 Drawing contours
  • 72. Prepared by Eng Shuaib [Type here] 900m 920m 900m 835m 835m 880m 900m 700m 1070m 800m 900m 800m 800m 1100m 970m 950m 875m 975m Presenter 2017-11-28 13:52:05 -------------------------------------------- Sometimes topographic maps are shown w i t hheight values at a given point, rather than contours. These are called ‘spot height’ maps and they are rather difficult to interpret. In order to get a better idea of the shape of the land surface the data can be contoured.
  • 73. Prepared by Eng Shuaib [Type here] The easiest way to draw a contour map based on spot heights is to simply interpolate between the known values. As you interpolate between points make sure you label the new values, as it quickly becomes very confusing if you don’t! Then join identical values with smooth curves to create contours that simulate topography 800m 800m Start by interpolating between individual points, labelling new values as you go. 750m 750m 700m 750m 800m Then join up all the original and interpolated points of equal value to form contours. 800m 850m 750m 700m
  • 74. Prepared by Eng Shuaib [Type here] 900m
  • 75. Prepared by Eng Shuaib [Type here] 900m 920m 875m 900m 800m 800m 700m 800m 1100m 970m 950m 900m 1070m 900m 880m 835m 835m 975m
  • 76. Prepared by Eng Shuaib [Type here] Completing the contouring exercise • Based on the contour map you have created: • Where is the highest ground? • Where is the lowest area? • Describe the major landforms • Mark on the most likely course of a stream and determine in which direction it is flowing Presenter 2017-11-28 13:52:06 -------------------------------------------- The highest ground is in the north ( > 1 1 0 0 m ) . The lowest area is in the SW, in the valley b o t t o m(<700m). The major landforms are a sinuous valley t h a ttrends SW-NE, then W-E, flanked by a broad ridge that trends NW-SE. The ground rises from the valley bottom to a high point in the north. The stream is flowing from east to west.
  • 77. Prepared by Eng Shuaib [Type here] 970m 1100m 975m 900m 800m 950 900 850 920m 800m 875m 835m 900m 880m 950m 900m 700m 1070m 835m Presenter 2017-11-28 13:52:07 -------------------------------------------- The highest ground is in the north ( > 1 1 0 0 m ) . The lowest area is in the SW, in the valley b o t t o m (<700m). The major landforms are a sinuous valley t h a ttrends SW-NE, then W-E, flanked by a broad ridge that trends NW-SE. The ground rises from the valley bottom to a high point in the north. The stream is flowing from east to west.
  • 78. Prepared by Eng Shuaib [Type here] 800m 900m
  • 79. Prepared by Eng Shuaib [Type here] Part 2 – Map interpretation • Contour patterns can be used to recognise distinctive landforms such as ridges, valleys and hills • Contours may appear as black or coloured lines on maps, and are often supported by colour shading to give an impression of relief • Cross-sections provide a useful way of visualizing the shape of the land surface, but care needs to be taken in their construction, particularly in terms of
  • 80. Prepared by Eng Shuaib [Type here] vertical exaggeration
  • 81. Prepared by Eng Shuaib [Type here] Previously we looked at the topography in this area – let’s take a closer look at the contours N 1 km © Crown Copyright/database right 2014. An Ordnance Survey/EDINA supplied service.
  • 82. Prepared by Eng Shuaib [Type here] 150m contour The contour interval is 10m with bold lines every 50m N © Crown Copyright/database right 2014. An Ordnance Survey/EDINA supplied service. What is the contour interval? 1 km
  • 83. Prepared by Eng Shuaib [Type here] Locate the 150m contour between Shottle and Blackbrook
  • 84. Prepared by Eng Shuaib [Type here] N © Crown Copyright/database right 2014. An Ordnance Survey/EDINA supplied service. If you walked along this contour, what would your route be like? 150m contour
  • 85. Prepared by Eng Shuaib [Type here] Flat, as long as you remain on the 150m contour
  • 86. Prepared by Eng Shuaib [Type here] Downhill 100m contour 150m contour N © Crown Copyright/database right 2014. An Ordnance Survey/EDINA supplied service. Which direction is downhill from the 150m contour? 200m contour
  • 87. Prepared by Eng Shuaib [Type here] N © Crown Copyright/database right 2014. An Ordnance Survey/EDINA supplied service. What else about the contours help to determine the direction
  • 88. Prepared by Eng Shuaib [Type here] of slope? The contour values are perpendicular to the slope, with the bottom of the number on the downhill side
  • 89. Prepared by Eng Shuaib [Type here] A B N © Crown Copyright/database right 2014. An Ordnance Survey/EDINA supplied service. What does the hillside look like if you stand at Point A 1 km
  • 90. Prepared by Eng Shuaib [Type here] and look towards Point B? It would go downhill to the stream and then uphill again to Point B
  • 91. Prepared by Eng Shuaib [Type here] A useful technique to visualise landforms is to draw a cross-section. This one is between Points A and B on the previous map No vertical exaggeration A B 200 100 Valley with stream 0 100 200 300 400 500 600 700 800 900 Distance (metres) This image shows a similar valley in the area, confirming the gentle slope angles Contour value (metres)
  • 92. Prepared by Eng Shuaib [Type here] The X axis represents distance and the Y axis height
  • 93. Prepared by Eng Shuaib [Type here] When drawing cross-sections it is important to be aware how the scales affect your perception of slope angle 2x vertical exaggeration A B 200 Valley with stream 100 0 100 200 300 400 500 600 700 800 Distance (metres) The purpose will dictate the scales you use. If the cross- section is to highlight relative changes in topography then a vertical exaggeration is fine, despite the fact that it increases the angles of all sloping lines If there is a need to add sub- surface geology or calculate true slope angles, then there should be no vertical exaggeration Contour value (metres)
  • 94. Prepared by Eng Shuaib [Type here] Compare the effects of vertical exaggeration on the same cross-section Notice how the change in vertical exaggeration affects the angles of slope Bear this in mind when drawing your own cross- sections and decide how much (if any) vertical exaggeration is required
  • 95. Prepared by Eng Shuaib [Type here] N © Crown Copyright/database right 2014. An Ordnance Survey/EDINA supplied service. You now know how to identify a sloping valley by the shape of Uphill
  • 96. Prepared by Eng Shuaib [Type here] the contours. They form a V-shape that points uphill
  • 97. Prepared by Eng Shuaib [Type here] Arrows indicate downhill direction of valleys N © Crown Copyright/database right 2014. An Ordnance Survey/EDINA supplied service. There are lots of valleys on the map; mark them with an arrow Presenter 2017-11-28 13:52:09 -------------------------------------------- This map shows some of the main valleys ( n o tall have been marked)
  • 98. Prepared by Eng Shuaib [Type here] pointing in the downhill direction
  • 99. Prepared by Eng Shuaib [Type here] Arrows indicate downhill direction of valleys N © Crown Copyright/database right 2014. An Ordnance Survey/EDINA supplied service. Notice that all the rivers are in valleys, but not all the valleys Presenter 2017-11-28 13:52:09 -------------------------------------------- There is no permanent water in these v a l l e y s ,however in the past there was sufficient water that flowed along these routes to cause erosion and form the valley. Is there any time in the recent geological past when there was greater water flow in this area?
  • 100. Prepared by Eng Shuaib [Type here] have a river. Why is this the case?
  • 101. Prepared by Eng Shuaib [Type here] N © Crown Copyright/database right 2014. An Ordnance Survey/EDINA supplied service. What feature do the contours in the red area represent? Presenter 2017-11-28 13:52:09 -------------------------------------------- Notice that the contours have a similars h a p e t oa valley, but the V-shape points downhill
  • 102. Prepared by Eng Shuaib [Type here] A broad, N-S trending ridge
  • 103. Prepared by Eng Shuaib [Type here] We can draw a cross-section to confirm our idea C D N © Crown Copyright/database right 2014. An Ordnance Survey/EDINA supplied service. It may help if you imagine you are standing at Point C on the 150m Axis of ridge Presenter 2017-11-28 13:52:09 -------------------------------------------- Answer: No; Point D is at the same height ( 1 5 0 m )as Point C, but the axis of the ridge is higher (at 175m).
  • 104. Prepared by Eng Shuaib [Type here] contour, looking towards Point D. Would you be able to see Point D?
  • 105. Prepared by Eng Shuaib [Type here] Cross-section showing the broad, gentle ridge between Points C and D 2x vertical exaggeration 200 100 C D Ridge Standing at Point C you would be unable to see Point D because the crest of the ridge is higher than Point D Here some vertical exaggeration is appropriate because 0 100 200 300 400 500 600 Distance (metres) the relief is very subtle Contour value (metres)
  • 106. Prepared by Eng Shuaib [Type here] Practical exercise 2 Constructing cross-sections
  • 107. Prepared by Eng Shuaib [Type here] Before constructing a cross- section, look at the contours and try to imagine what the surface topography looks like Narrower range of contours between 140-160m indicate a relatively flat hill top Widely spaced contours showing less steep slopes compared to those in the east Closely spaced contours showing a steep slope A A’ We will now draw our own cross- section between Cowers Lane (A) and Chevinside (A’)
  • 108. Prepared by Eng Shuaib [Type here] Label each contour height and plot the value directly onto the Y-axis of the cross-section A 200m A’ 150m 100m 50m Use graph paper to mark on every time a contour crosses the chosen line of section 110 105 100 95 90 85
  • 109. Prepared by Eng Shuaib [Type here] This surface should be drawn free hand to give a natural shape that honours the contours A 200m A’ 150m 100m 50m 4x vertical exaggeration Once all the contour heights along the section have been plotted the land surface can be added
  • 110. Prepared by Eng Shuaib [Type here] A A’ 4x vertical exaggeration East West A completed cross-section between A-A’ The vertical scale has been exaggerated in order to show the subtle relief. To calculate the vertical exaggeration, divide the horizontal scale (1cm to 200m) by the vertical scale (1cm to 50m) So, 200/50 = 4x vertical exaggeration 200m 150m 100m 50m 0 1 km 2 km 3 km
  • 111. Prepared by Eng Shuaib [Type here] Scale 1: 20 000
  • 112. Prepared by Eng Shuaib [Type here] Comparison between a vertically exaggerated section and a true scale cross-section 200m 150m 100m 50m 0 200m 0 No vertical exaggeration 4x vertical exaggeration
  • 113. Prepared by Eng Shuaib [Type here] The vertically exaggerated section provides a clearer representation of subtle landforms, the other a true representation of slope angles
  • 114. Prepared by Eng Shuaib [Type here] Learning outcomes You have now been introduced to the basic elements of topographic maps You have used contours to identify common landforms and begun to visualise them in 3-D You can now construct cross-sections and understand the concept of vertical exaggeration
  • 115. Prepared by Eng Shuaib [Type here] Handouts required for the practicals Slide 50: print out at A4, in B/W, portrait format Slide 51: print out at A4, in colour, portrait format Slide 52: print out at A4, in colour, portrait format Graph paper for constructing the cross-section
  • 116. Prepared by Eng Shuaib [Type here] 975m 900m 920m 900m 835m 835m 880m 900m 700m 1070m 800m 900m 800m 800m 1100m 970m 950m 875m
  • 117. Prepared by Eng Shuaib [Type here] N © Crown Copyright/database right 2014. An Ordnance Survey/EDINA supplied service. 1 km
  • 118. Prepared by Eng Shuaib [Type here] A A’
  • 119. Prepared by Eng Shuaib [Type here]