2012 SPRING
JEM 104
Introduction to
Surveying and Mapping
Dr. Veysel Işık
Chapter 5
THE METHODS OF
RELIEF
REPRESENTATION
A/Professor
Ankara University
Dept. of Geological Engineering
Tectonics Research Group
JEM 104 Introduction to Surveying and Mapping
Introduction
Relief (or Terrain) is an essential aspect of physical geograghy.
Because the earth’s surface is seldom absolutely flat, map makers have always
been challenged to convey information about its undulations to map user.
And because maps are drawn or
printed on flat sheets of papers,
they are not particularly wellsuited to representing a threedimensional surface.
On flat paper maps, relief
(terrain) can be depicted in a
variety of ways
Veysel Işık
JEM 104 – Int. To Surveying and Mapping
Symbols
Contour lines
Contour lines are an effective device for representing relief on topographic
maps. They can be defined as an imaginary line connecting points of equal
elevation on the ground surface.
As with all types of
isolines, when contour
lines are close together,
they represent a steep
slope, whereas when
lines are far from each
other, they represent a
gradual slope.
Every fifth or tenth
contour starting at sea
level is an index contour,
which is drawn as a
heavier line and is
labelled.
Veysel Işık
JEM 104 – Int. To Surveying and Mapping
Each topographic map uses a contour interval, or equidistance, (the distance in
elevation between contour lines) appropriate for that area. This is called
contour interval (The basic contour interval is the vertical distance contours).
While flat areas may be mapped with a 5 meter contour interval, stepped
terrain may have a 20 meter or more contour interval. This is why the contour
interval is still specified on the topographic map legend.
Characteristics of contour lines are:
Veysel Işık
JEM 104 – Int. To Surveying and Mapping
1.Connect point of equal elevation.
2.Always connects close contour
lines. This is not always visible on the
map.
3.They never cross, split or intersect
– at a cliff they might merge.
4.Evenly spaced contour lines
indicate a uniform slope.
5.Closely spaced contour lines show
a steep slope.
6.Widely spaced contour lines show
gentle slope.
7.Uneven spacing – irregular or
variable slope.
9.Closed contours with arrow in the
centre represent depressions.
Researh and learn
“Types of Contours”
Veysel Işık
JEM 104 – Int. To Surveying and Mapping
In the following exercise, you have to find out which topographic
isolines (contours) representation matches which profile.
A
B
?
Veysel Işık
JEM 104 – Int. To Surveying and Mapping
C
?
E
D
?
?
?
Spot Heights
Another method of relief
representation is the use of spot
heights that indicate that the
elevation of points on the Earth’s
surface.
This has the advantage that exact
values provided at identifiable
locations.
However, it does not provide
useful information about the shape
of terrain between the spot
heights, nor does it provide any
visual, three-dimensional effect.
Veysel Işık
JEM 104 – Int. To Surveying and Mapping
Hill Shading
The most visually effective method of relief representation is hill shading. It is
also known as plastic shading, relief shading and terrain shading.
Hill shading is simply the application of gray values to the maps to simulate
shadows that make modelling of the surface apparent.
The light is angled so that it
strikes obliquely, from the
upper-left corner of the model,
and shadows are cast toward the
lower right.
This method is often combined
with contours and spot heights
so that measurements are
available, in addition to the
visaul effect.
Veysel Işık
JEM 104 – Int. To Surveying and Mapping
Contour Interpretation
Countour lines are particularly
useful for terrain analysis.
The horizontal spacing of
contour reveals the nature of the
slope.
Uniform, gently slope
Uniform, steep slope
If the contours are evenly spaced,
for example, the slope is uniform.
Widely spaced contours indicate
a relatively flat slope, and closely
spaced contours a steep one.
If contours are closely spaced at
the top of a slope and widely
spaced at the bottom, the slope
has a concave shape.
If contours are closely spaced at
the bottom and widely spaced at
the top, the slope is convex.
Veysel Işık
JEM 104 – Int. To Surveying and Mapping
Concave slope
Convex slope
Countour reflect other aspects of the terrain.
Water-cut stream valleys, for
example, usually have a Vshaped cross-section,
whereas glacial valleys are
rounded into a U-shaped.
Contours that cross valleys
point in the upstream
direction, but those that cross
ridges or drainage divides
point downslope.
The shapes of ridges, valleys,
hills, and depressions, as
well as the charactersitics of
slopes, are indicated by the
arrangement of contour
lines.
Veysel Işık
JEM 104 – Int. To Surveying and Mapping
Elevations of locations are estimated by means of linear interpolation
between countour.
This process is based on the assumption that the slope between contours is
constant.
As it is seen in figure, draw a line through the point whose
elevation is to be obtained, in the direction of maximum slope (that
is, at a right angle to the contour lines). Next, determine the point’s
distance from the lower contour as a proportion the total distance
between the two contours. Then apply that proportion to the
contour interval. Finaly add the resulting fraction of the contour
interval to the lower contour elevation to obtain the point’s
estimated elevation.
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JEM 104 – Int. To Surveying and Mapping
Profiles, which are cross-sectional
views through the terrain, provide
information about slope steepness,
intervisibility, and so on and are
used in planning, construction
projects.
Drawing a profile begins with the
selection of starting and ending
point that fit the needs of the task
at hand.
Once these points are selected, a
cut-line joining them is drown on
the map
The next step in creating the
profiles involves the selecting of
the vertical scale.
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JEM 104 – Int. To Surveying and Mapping
Assume, as an example, that the
map from which the profile is
being taken has a scale of 1:10,000,
which is a relatively large scale.
This means that each horizontal
centimeters on the map represents
10,000 centimeters or 100 meters
on the ground.
If the same scale is used for the
vertical dimensions on the profile,
the rise of 100 meters is similarly
represented by a vertical
dimension of 1 centimeter.
The use of a vertical scale that is
greater than the horizontal scale of
a cross-section or model is called
vertical exaggretation.
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JEM 104 – Int. To Surveying and Mapping
When the desired vertical
exaggeration has been chosen, the
next step is to prepare the profile
itself.
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JEM 104 – Int. To Surveying and Mapping
The surface of the terrain typically rises and falls; two terms are
commonly used to describe surface variations: slope and gradient.
Slope is measure of the vertical difference in the elevation of a surface at
two different points.
Slopes are expressed as rations, fractions, persentager, or degrees. The
measure of a slope is based on the relationship between the rise and the
run.
Veysel Işık
JEM 104 – Int. To Surveying and Mapping
Topographic Features
Topography is the surface configuration of the earth resulting from complex
interactions of natural processes.
As a major environmental element, topography has direct and indirect effects on
human life.
Drainage patterns, the arragements of streams on the landscape, are indicators of
underlying geology.
main
stream
tributaries
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JEM 104 – Int. To Surveying and Mapping
The term dentritic means
treelike, whch is characterized
by treelike branch.
This drainage patterns
are variation of the
dentritic type.
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JEM 104 – Int. To Surveying and Mapping
Another modification of
the dentritic pattern is
trellis drainage pattern,
which has parallel
tributaries.
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JEM 104 – Int. To Surveying and Mapping
A circular pattern of channels
flowing away from, or toward, a
central point is called a radial
drainage pattern.
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JEM 104 – Int. To Surveying and Mapping
The underlying
topograpgy control the
forming of annular
drainage pattern.
Veysel Işık
JEM 104 – Int. To Surveying and Mapping