Contouring

Presentation Of Surveying
And Drawing

Submitted to:
Honourable Respected Sir
Mansoor Awan

Bs Applied Geology
4th Semester
Session 2016-2020
Institue Of Geology
UAJK Muzaffarabad
Pakistan

 Contours
A Contour is an imaginary line on the ground joining
the points of equal elevation or reduced level.
 Contour line
A contour line is a line on the map representing a
contour.

 Contour interval
The vertical distance between two successive contours is
known as ‘Contour interval’. It remains constant for
a given map. The difference in R.L.’s of two contour
gives contour interval.

 COMMON VALUES OF THE CONTOUR -
INTERVAL
i) For large scale maps of flat country, for building
sites, for detailed design work and for calculation of
quantities of earth work; 0.2 to 0.5 m.
ii) For reservoirs and town planning schemes;
0.5 to 2m.
iii) For location surveys. 2 to 3m.
iv) For small scale maps of broken country and general
topographic work; 3m,5m,10m,or 25m.

 Horizontal equivalent
The horizontal distance between two successive contours
is known as ‘Horizontal equivalent’. It is not constant
for a given map, it varies according to the steepness
of the ground.

 Methods of Contour Surveying
 There are two methods of contour surveying:
 Direct method
 Indirect method

Direct Method of Contouring
 It consists in finding vertical and horizontal controls of
the points which lie on the selected contour line.

 For vertical control levelling instrument is commonly used. A level is set on a
commanding position in the area after taking fly levels from the nearby bench mark.
The plane of collimation/height of instrument is found and the required staff reading
for a contour line is calculated.
 The instrument man asks staff man to move up and down in the area till the required
staff reading is found. A surveyor establishes the horizontal control of that point using
his instruments.
 After that instrument man directs the staff man to another point where the same staff
reading can be found. It is followed by establishing horizontal control.
 Thus, several points are established on a contour line on one or two contour lines and
suitably noted down. Plane table survey is ideally suited for this work.
 After required points are established from the instrument setting, the instrument is
shifted to another point to cover more area. The level and survey instrument need not
be shifted at the same time. It is better if both are nearby to communicate easily.
 For getting speed in levelling some times hand level and Abney levels are also used.
This method is slow, tedious but accurate. It is suitable for small areas.

Indirect Method of
Contouring
In this method, levels are taken at some
selected points and their levels are
reduced. Thus in this method horizontal
control is established first and then the
levels of those points found.
After locating the points on the plan,
reduced levels are marked and contour
lines are interpolated between the selected
points.
For selecting points any of the following
methods can be used:
1.Method of squares
2. Method of cross-section
3. Radial line method

Method of Squares
In this method area is divided into a number of squares and all
grid points are marked
Commonly used size of square varies from 5 m × 5 m to 20 m ×
20 m. Levels of all grid points are established by levelling. Then
grid square is plotted on the drawing sheet. Reduced levels of
grid points marked and contour lines are drawn by interpolation

Commonly used size of square varies from
5 m × 5 m to 20 m × 20 m. Levels of all
grid points are established by levelling.
Then grid square is plotted on the drawing
sheet. Reduced levels of grid points
marked and contour lines are drawn by
interpolation

Method of Cross-Section
In this method cross-sectional points are taken at regular
interval. By levelling the reduced level of all those points are
established. The points are marked on the drawing sheets,
their reduced levels (RL) are marked and contour lines
interpolated.

Figure 2 shows a typical planning of this work. The spacing of
cross-section depends upon the nature of the ground, scale of
the map and the contour interval required. It varies from 20 m to
100 m. Closer intervals are required if ground level varies
abruptly.
The cross- sectional line need not be always be at right angles to
the main line. This method is ideally suited for road and railway
projects.

Radial Line Method
In this method several radial lines are taken from a point in the area. The
direction of each line is noted. On these lines at selected distances points
are marked and levels determined. This method is ideally suited for hilly
areas. In this survey theodolite with tacheometry facility is commonly used.

Drawing Contours
After locating contour points smooth contour lines are drawn
connecting corresponding points on a contour line. French curves
may be used for drawing smooth lines. A surveyor should not lose
the sight of the characteristic feature on the ground. Every fifth
contour line is made thicker for easy readability. On every contour
line its elevation is written. If the map size is large, it is written at
the ends also.

Contour Maps and Its Uses
A contour maps consists of contour lines which are imaginary lines
connecting points of equal elevation. Such lines are drawn on the plan of
an area after establishing reduced levels of several points in the area.
The contour lines in an area are drawn keeping difference in elevation of
between two consecutive lines constant. For example, the contour map in
fig. 1 shows contours in an area with contour interval of 1 m. On contour
lines the level of lines is also written.

In cartography, contour lines are an imaginary line of a terrain that
joins the point of equal elevation above a given level, such as mean
sea level or benchmark.
Contours Lines

Characteristics of Contour
Lines in Surveying

Following are the characteristics of contour
lines in surveying for reading contour
maps:
No two lines meet on intersect each
other in any case.
All lines close themselves within the map
boundaries or outside it.
If the contour lines are very close to
each other, this indicates steep slope.
If the contour lines are at very large
distance to each other, this indicates a
gentle slope.
If the closed lines have higher elevation
in the center then it represents the hill or
mountain.
If the closed line have increasing
elevation as we move away, then it
represents a pond or a depression in the
ground profile.
In a single contour line, at any point the
elevation is same.

Types of Contour Lines in
Surveying and their
Importance
Contour lines are differentiated into many
types based upon the function it denotes,
they are listed as below:
Isopleth
Isohyet
Isobar
Isobath
Isohaline
Isotherm
Isohel
Isohume
Isoneph
Isopectic
Isotach
Isogeotherm

Isopleth
Isopleth on a contour map connects the places having
the same value of some measurable quantity of
geographical or meteorological phenomena. For Ex. The
population density of an area can be calculated by the
quotient of population in the area and surface area of a
region

Isohyet
Isohyet indicates the points of equal rainfall
of an area in the given time.
Contour Lines - Isohyet

Isobar
Isobars on contour maps indicates the point of equal or
constant atmospheric pressure for a given period.
This type of contour is used in the prediction of future
weather patterns isobars are commonly used in television
weather reporting.

Isobath
It is a type of imaginary contour lines on a map of chart that
connects all the points having same depth below water
surface like ocean, sea and lake.

Isohaline
It is a type of contour lines on a map which connect the point of
equal salinity in the water body (majorly contour)

Isotherm
It is a type of contour lines on a map of chart with connects the
point of equal temperature of a given area.
Further they are divided into two types.
Isocheim: It is a line of equal mean winter temperature.
Isothere: It is a line of equal means summer temperature.
An isotherm at 0 degree is called freezing level

Isohel
It is a type of contour lines on a map that connects the
places of equal duration of sunshine for a given period.

Topographic Maps and Cross-sections
Let's pretend we are going on a class field trip to an imaginary location known as
Armadillo Ridge. Before we get there, we want to determine the easiest way to
the top. To help us, we will use a topographic map of Armadillo Ridge to make a
cross-section showing us a side view of the land.
When looking at a flat map, there is always a compass rose indicating the
cardinal directions: North, South, East and West. A topographical map has an
extra feature; it has lines of equal elevation that loop around the map. These are
contour lines. They can never cross because there can't be a location that has
two different elevations!
We can use a topographical map to make a cross-section along any straight line
we draw on the map. A cross-section will give us an idea of how the terrain looks
from a side view.
Let's first look at a topographical map of Armadillo Ridge

Any location along the 100-foot line is 100 feet above sea-
level. The same goes for the other contour lines respectively.
The bold line drawn across the map starting with A and ending
at A' (A-prime) is the cross-section we are going to draw.
You may be wondering why the right-side of the map is cut off.
This is normal. A map can be made for a very specific location,
and the terrain to the east was not necessary to include in the
map of Armadillo Ridge.

Making a Cross-section
Step 1:
Take a thin strip of paper and place it along the cross-
section line. Where the contours intersect with the strip of
paper, make a mark and record the elevation. These marks
and elevations are shown in red.

Step 2:
Take that strip of paper and put it on a fresh piece of paper. Draw two vertical lines
(similar to two y-axes on a graph) representing the boundaries of your cross-section.
Also, draw equally spaced elevation lines parallel to your strip of paper. These lines
would be parallel to the x-axis on a graph and are labeled with numbers representing
elevations. It looks nice if you make the bottom line 50 feet below your lowest
elevation and your top line 50 feet above your highest elevation.
Take that strip of paper and put it on a fresh piece of paper. Draw two vertical lines
(similar to two y-axes on a graph) representing the boundaries of your cross-section.
Also, draw equally spaced elevation lines parallel to your strip of paper. These lines
would be parallel to the x-axis on a graph and are labeled with numbers representing
elevations. It looks nice if you make the bottom line 50 feet below your lowest
elevation and your top line 50 feet above your highest elevation.

Step 3:
Draw dots corresponding to the elevations along the strip of
paper representing the cross-section line.

Step 4:
Draw a smooth line connecting the dots. This is for artistic reasons, to
some extent. We really don't know what the terrain looks like between
the contour lines, so we make a rough estimation of what it might look
like.

 CHARACTERISTICS OF CONTOURS
i) All points in a contour line have the same
elevation.
ii)Flat ground is indicated where the contours are
widely separated and steep- slope where they run close
together.

iii) A uniform slope is indicated when the contour lines
are uniformly spaced and


Iv.A plane surface when they are straight, parallel and equally
spaced.

Concave Slopes
 On small concave slopes, there is sometimes enough
compressive support from the bottom to prevent
hard-slabs from releasing but on medium to large
slopes, compressive support plays very little role.

STEPPED SLOPE
This taper may be defined by a continuous straight line slope of
the outer surface of the elongated body, or a stepped slope
formed from a series of interconnected cylindrical portions of the
elongated body which increase in diameter from the front end to
approximately midway on the elongated body of the vibrator
head.

Convex Slope
A terrain feature that is curved or rounded like the exterior of a
sphere or circle, i.e. goes from less steep to more steep. Convex
slopes generally tend to be less safe than concave slopes, but
concave slopes can also avalanche.
Slope Shape:
Whether a slope is concave, convex, or planar makes some
difference in avalanche danger, usually not a significant
difference. Avalanches happen on any steep slope without thick
anchors despite the shape of the slope. Slope shape makes
more difference on smaller slopes than on larger ones

Cuesta
 A cuesta is a hill or ridge with a gentle slope on one
side, and a steep slope on the other. In geology the
term is more specifically applied to a ridge where a
harder sedimentary rock overlies a softer layer, the
whole being tilted somewhat from the horizontal. This
results in a long and gentle backslope called a dip
slope that conforms with the dip of resistant strata,
called caprock. Where erosion has exposed the
frontslope of this, a steep slope or escarpment occurs.
The resulting terrain may be called scarpland.

plateau
 a land area having a relatively level surface
considerably raised above adjoining land on at least
one side, and often cut by deep canyons.

v) A series of closed contour lines on the map represent a
hill , if the higher values are inside
60
65
70
75
80
60
65
70
75
80
HILL

A Conical hill:
 A conical hill (also cone or conical mountain) is a
landform with a distinctly conical shape. It is usually
isolated or rises above other surrounding foothills, and is
often, but not always, of volcanic origin.
 Conical hills or mountains occur in different shapes and
are not necessarily geometrically-shaped cones; some are
more tower-shaped or have an asymmetric curve on one
side. Typically, however, they have a circular base and
smooth sides with a gradient of up to 30°. Such conical
mountains are found in all volcanically-formed areas of
the world such as the Bohemian Central Uplands in the
Czech Republic, the Rhön in Germany or the Massif
Central in France.

Round Top Hill:
 Round Top is a boulder-strewn hill notable as the
topographic high point[7]:3 of the Gettysburg
Battlefield and for 1863 American Civil War
engagements for which Medals of Honor were
awarded. In addition to battle monuments, a historic
postbellum structure on the uninhabited hill is the Big
Round Top Observation Tower Foundation Ruin.

vi) A series of closed contour lines on the map indicate a
depression if the higher values are outside
70
60
65
70
75
80
DEPRESSION
60
65
70
75

x) Contour lines cannot merge or cross one another on
map except in the case of an overhanging cliff.
40 30 20 10
OVERHANGING CLIFF
10
20
30
40

xi) Contour lines never
run into one another
except in the case of a
vertical cliff. In this
case ,several contours
coincide and the
horizontal equivalent
becomes zero.
CHARACTERISTICS OF CONTOURS
403020
50OVERHANGING CLIFF
10
20
30
40
VERTICAL
CLIFF
50
10 50

CHARACTERISTICS OF CONTOURS
Xii) Depressions between
summits is called a
saddle. It is represented
by four sets of contours
as shown. It represents a
dip in a ridge or the
junction of two ridges.
SADDLE70
80
90
70
80
90
110
100
90

A Pass:
 pass is a navigable route through a mountain range or
over a ridge. Since many of the world's mountain
ranges have presented formidable barriers to travel,
passes have played a key role in trade, war, and both
human and animal migration throughout Earth's
history. At lower elevations it may be called a hill pass.
The highest vehicle-accessible pass in the world
appears to be Mana Pass, located in the Himalayas on
the border between India and Tibet, China.

A Col:
 A col is a saddle-like gap in an arete. It is formed by
headward erosion of two glacier cirques towards each
other which carve a gap in an arete.

A Gap:
 A gap is a low area between two higher-elevation
landmasses, such as mountains. Gaps are similar to
passes, but more rugged and difficult to navigate.

 The most rugged gaps are often called "notches."
Notches are rarely crossed, and usually marked by steep
cliffs on either side.

 Another name for a gap is a "saddleback," because wide
gaps often have the shape of a saddle. There are peaks on
almost every continent called Saddleback Mountain:
Saddleback Mountain, Maine; Saddleback Mountain,
Arizona; and Saddleback Mountain, Australia, are just a
few

A Knoll:
 A Knoll is a low isolated hill which is shown on a
contour map with a ring contour pattern. In
topographic maps every 5th contour line is drawn in
bold print or wider than other contours. Such lines are
called index contour lines.

Ridges:
 Contour ridges are small earthen ridges, 15 to 20 cm
high, with an upslope furrow which accommodates
runoff from a catchment strip between the ridges

A Valley:
 A valley is an elongated depression in the landscape
that is formed by the action of water (V-shaped) or
carved out by glaciers (U-shaped). Valley bottoms are
represented by "U" or "V" shaped contour lines with
their closed end pointing towards higher elevation.

A SpUR:
 A spur is a short, continuous sloping line of higher
ground, normally jutting out from the side of a ridge. A
spur is often formed by two roughly parallel streams
cutting draws down the side of a ridge. ... Contour lines
on a map depict a spur with the U or V pointing away
from high ground

Interlocking Spur:
 An interlocking spur, also known as an overlapping
spur, is one of any of a number of projecting ridges
that extend alternately from the opposite sides of the
wall of a young, V-shaped valley down which a river
with a winding course flows. Each of these spurs
extends laterally into a concave bend of the river such
that when viewed either upstream or from overhead,
the projecting ridges, which are called spurs, appear to
"interlock" or "overlap" in a staggered formation like
the teeth of a zipper

A Gorge:
 They are deep and narrow river valleys with very steep
sides. A gorge is represented by very closely-spaced
contour lines on a map with the innermost contour
showing small gap between its two sides. A tongue of
land, projecting from higher ground into the lower is
called a spur.

INTERPOLATION OF CONTOURS
There are three main methods of interpolation:
i) By Estimation:- The position of the contour
points between ground - points are estimated
roughly and the contours are then drawn
through these points. This is a rough method
and is suitable for small scale maps.
ii) By arithmetical calculation:- This is very
tedious but accurate method and is used for
small areas where accurate results are
necessary. The contours are interpolated as
under:

ii) By arithmetical calculation:-

Now consider the ADMP is surveyed plot, then whole area
is divided into no.of squares and RL are plotted at every
spot. Then if the required contour is 89.000m, then consider
small square ABGH.

Then the difference in elevation between A &B is
(90.895 – 88.420 = 2.475m) in distance of 5m. Then by
similar triangle method.
0.58/x = 2.475/5, x = 1.17m from point A.
Similarly of point A& H
0.58/x = 2.135/5, x = 1.358m from point A.
Then plot 89.000m contour by scale.

Observation table
S.N. OBSERVATION RISE FALL RL REMARKS
BS IS FS
1.800 100.000 BM
1 1.115
2 1.100
3 0.990
4 0.890
5 0.800
6 0.525
7 0.950
8 0.755 1.000 CP 1
9 1.170
10 1.115
11 2.000
12 1.995
12 1.995
CHECK :- ƩBS – ƩFS = ƩRISE – ƩFALL = LAST RL – FIRST RL.

BS IS FS
12 1.995
12 1.995
13 1.190
14 0.900
15 1.890
16 1.800
17 0.925
18 0.950
19 1.755 1.500 CP 2
20 2.170
21 2.115
22 1.350
23 0.900
24 0.995
24 0.995

BS IS FS
24 0.995
24 0.995
25 1.190
26 0.900
27 1.890
28 1.800
29 0.925
30 0.950
31 1.755 1.500 CP 2
32 2.170
33 2.115
34 1.350
35 0.900
36 1.115
36 1.115

BS IS FS
36 1.115
36 1.115
37 1.290
38 1.900
39 0.890
40 1.450
41 0.925
42 1.950
43 1.755 1.500 CP 3
44 1.170
45 2.115
46 1.300
47 1.900
48 0.995

Uses Of Contours:
 Contour maps are extremely useful for various engineering works:
 A civil engineer studies the contours and finds out the nature of the ground
to identify. Suitable site for the project works to be taken up.
 By drawing the section in the plan, it is possible to find out profile of the
ground along that line. It helps in finding out depth of cutting and filling, if
formation level of road/railway is decided.
 Intervisibility of any two points can be found by drawing profile of the
ground along that line.
 The routes of the railway, road, canal or sewer lines can be decided so as to
minimize and balance earthworks.
 Catchment area and hence quantity of water flow at any point of nalla or
river can be found. This study is very important in locating bunds, dams and
also to find out flood levels.
 From the contours, it is possible to determine the capacity of a reservoir.
92

Contouring

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