Table of Contents

Contour | Method of Contour Surveying | Contour Interval | Gradient | Direct Method | Indirect Method | Contour Map & Uses.

What is Contour?

Contour can refer to several things depending on the
context, but in general, it refers to a line or shape that represents the
outline or boundary of an object or surface.

In geography and cartography, contour lines are lines that connect
points of equal elevation on a map or chart, allowing the shape and elevation
of the terrain to be visualized.

In art, contour refers to the line that defines the edge of
a form or shape, often used to create the illusion of depth and volume.

In makeup, contouring involves using makeup to shade and
highlight areas of the face to create the appearance of more defined features.

In engineering and manufacturing, a contour refers to a
shape or profile that is carefully designed to achieve a specific function or
aesthetic effect. [ Chain Surveying ]

Contouring is a technique of creating a smooth
transition between two different shapes, surfaces or textures.

What is Contour Surveying.

Contour surveying
is a type of land surveying that involves mapping and measuring the elevation
of the land surface to create contour lines on a topographic map. Contour lines
connect points of equal elevation, creating a two-dimensional representation of
the three-dimensional shape of the land. [ Surveying Objective Question ]

Contour surveying
is typically used to create topographic maps that show the shape, slope, and
elevation of the land. This information can be useful in a variety of
applications, including civil engineering, urban planning, and environmental
studies.

During a contour
survey, surveyors use specialized equipment to measure the elevation of the
land at specific points, such as using a total station or a GPS receiver. This
data is then used to create a contour map, which can be used to analyze the
terrain, plan construction projects, or make decisions about land use.

Overall, contour
surveying is an important technique for understanding and analyzing the
physical features of the land, and it plays a crucial role in many fields that
rely on accurate geographic information.

Application
of contour surveying in civil engineering.

Contour surveying
plays an important role in civil engineering by providing accurate information
about the topography and shape of the land, which is essential for planning and
designing infrastructure projects. Some of the key applications of contour
surveying in civil engineering include:

Site analysis and
selection – Contour surveys can help civil engineers assess the suitability of a
site for a particular project, such as a road, bridge, or building. The survey provides
information about the topography and slope of the land, which can help
engineers determine whether the site is suitable for construction and identify
potential challenges.

Grading and
earthwork – Contour surveys can be used to determine the optimal grading and
earthwork requirements for a construction project. By analyzing the contours of
the land, civil engineers can identify areas that need to be filled or
excavated to create a level surface for construction.

Drainage and
erosion control – Contour surveys can also help engineers design effective
drainage and erosion control systems for a construction site. By analyzing the
slope and shape of the land, engineers can identify areas that are prone to
erosion or flooding and develop strategies to mitigate these risks.

Road and highway
design – Contour surveys are essential for designing roads and highways that are
safe, efficient, and cost-effective. The survey provides information about the
terrain, including hills, valleys, and curves, which can be used to design a
roadway that is suitable for the local conditions.

Overall, contour
surveying is a valuable tool for civil engineers, providing critical
information that is essential for planning and designing infrastructure
projects that are safe, functional, and sustainable.

What is Contour Gradient.

Contour gradient
refers to the rate of change of elevation along a contour line on a topographic
map. It is a measure of how steeply the land is sloping at a particular point
along the contour.

The contour
gradient is typically expressed as a percentage or a ratio. For example, a
contour gradient of 5% means that the land is rising or falling 5 vertical
units for every 100 horizontal units. A contour gradient of 1:20 means that for
every 20 units of horizontal distance, the land rises or falls by 1 unit of
vertical distance.

The contour
gradient is important in many applications, such as civil engineering,
environmental management, and land use planning. Engineers use the contour
gradient to design infrastructure projects such as roads, highways, and bridges
that are safe and functional for the local conditions. Environmental managers
use the contour gradient to identify areas that are prone to erosion or
landslides, and to develop strategies to mitigate these risks. Land use
planners use the contour gradient to identify areas that are suitable for
different types of land use, such as agriculture, forestry, or urban
development.

The
contour gradient is a valuable tool for understanding the shape and slope of
the land, and it plays an important role in many fields that rely on accurate
geographic information.

Contour Line

A contour line is a
type of line that connects points of equal elevation on a topographic map or
chart. The contour line represents a specific elevation above sea level, and it
helps to show the shape and slope of the terrain. [ Surveying Objective Question ]

Contour lines are
typically used to create topographic maps that provide a three-dimensional
representation of the land surface. The contour lines are usually drawn at
regular intervals, such as every 10 or 20 meters, and they are labeled with
their corresponding elevation. On a topographic map, the contour lines form a
series of closed loops, with the innermost loops representing higher elevations
and the outermost loops representing lower elevations.

Contour lines can
provide valuable information about the terrain, such as the location of hills,
valleys, ridges, and depressions. By analyzing the contour lines, map readers
can determine the slope and steepness of the land, as well as the direction of
water flow. [ Types of Chain Surveying ]

Note – Contour
lines are an essential tool for understanding the shape and topography of the
land, and they are used in a variety of applications, including civil
engineering, environmental management, and land use planning.

Characteristic Of Contour Line

Contour lines have
several characteristics that make them useful for representing the shape and
elevation of the land on a topographic map. Some of the key characteristics of
contour lines include:

Constant elevation – Each contour line represents a specific elevation above sea level, and all
points along the line have the same elevation. The elevation of each contour
line is usually labeled on the map.

Closed loops – Contour lines are typically drawn as closed loops, which means that they do not
cross or intersect each other. The innermost loop of a series of contour lines
represents the highest elevation, while the outermost loop represents the
lowest elevation.

Uniform spacing – Contour lines are usually drawn at regular intervals, such as every 10 or 20
meters. The spacing between contour lines indicates the steepness of the
terrain: closer contour lines indicate steeper slopes, while wider spacing
indicates gentler slopes.

Orientation – Contour lines follow the shape of the land and are oriented in the direction of
the slope. For example, contour lines that represent a ridge or hill will be
roughly circular or oval, while contour lines that represent a valley or
depression will be roughly U-shaped.

Index contours – Certain contour lines, called index contours, are drawn with a thicker or
darker line weight and are labeled with their elevation. These contour lines
are typically drawn at larger intervals, such as every 50 or 100 meters, and
provide a quick reference for the overall shape of the land. [ Surveying Objective Question ]

Contour Interval

Contour interval
refers to the vertical distance between adjacent contour lines on a topographic
map. It represents the difference in elevation between two adjacent contour
lines, and it is typically measured in feet or meters.

Hill ( contour )

The contour
interval is an important factor in creating a topographic map, as it determines
the level of detail and accuracy of the map. A smaller contour interval, such
as 5 meters, indicates a greater amount of detail, as there are more contour
lines on the map to represent smaller changes in elevation. A larger contour
interval, such as 50 meters, indicates less detail, as there are fewer contour
lines on the map to represent larger changes in elevation.

The contour
interval is usually chosen based on the purpose of the map and the
characteristics of the terrain being mapped. For example, a map of a
mountainous area may require a smaller contour interval to accurately represent
the steep slopes and changes in elevation, while a map of a flatter area may be
adequately represented with a larger contour interval.

The
contour interval is an important factor in creating accurate and detailed topographic maps, and it plays a crucial role in many applications, such as
civil engineering, environmental management, and land use planning.

Factor Affecting Contour Interval.

There are several
factors that can affect the choice of contour interval for a topographic map.
Some of these factors include:

Scale of the map – The scale of the map determines the level of detail that can be represented,
and it can affect the choice of contour interval. A larger scale map can
support a smaller contour interval, allowing for greater detail in the
representation of the terrain.

Steepness of the
terrain – The steepness of the terrain is an important consideration when
choosing a contour interval. In areas with steep slopes, a smaller contour
interval may be required to accurately represent the changes in elevation. [ Surveying MCQ ]

Size of the area
being mapped – The size of the area being mapped can also affect the choice of
contour interval. A larger area may require a larger contour interval to
prevent the map from becoming too cluttered with contour lines.

Availability of
data – The availability of elevation data can also affect the choice of contour
interval. If elevation data is only available at a coarse resolution, a larger
contour interval may be necessary to avoid creating a map with inaccurate or
misleading information.

Purpose of the map – The purpose of the map can also affect the choice of contour interval. For
example, a map intended for hiking or mountaineering may require a smaller
contour interval to provide greater detail and accuracy for navigation, while a
map intended for land use planning may require a larger contour interval to
show the broader patterns of the terrain.

The choice
of contour interval for a topographic map depends on a variety of factors, and
careful consideration of these factors is necessary to create an accurate and
useful map.

Method Of Contour Surveying.

1. Direct Method
2. Indirect Method

Direct Method

In contour
surveying, the direct method of locating contours involves physically measuring
the elevation of points on the terrain using a surveying instrument such as a
level or a total station. The direct method is typically used when a high level
of accuracy is required and when the terrain is relatively flat or has simple
contours.

To use the direct
method, the surveyor sets up the instrument at a known point and takes a
measurement of the elevation at that point. The surveyor then moves to another
point and takes a measurement of the elevation at that point. The elevation
difference between the two points is then calculated and used to determine the
slope between the two points. This process is repeated at various locations
across the terrain, and the elevations and slopes are used to create a contour
map. [ Surveying Objective Question ]

The direct method
can be time-consuming and requires a high level of skill and expertise from the
surveyor, as well as careful attention to detail. However, it can produce
highly accurate results and is often used in engineering and construction
projects where accuracy is critical.

Indirect Method

The indirect method
of contour surveying is a technique used to determine the contour lines of a
piece of land when direct measurement of elevation is not possible or
practical. This method involves the use of topographical maps and photographs
to estimate the elevation of the land surface and to draw the contour lines.

1. Square Method
2. Cross Section Method
3. tacheometric method

Square Method

Indirect method of contour surveying in square method.

The indirect method
of contour surveying using the square method is a technique that is used to
estimate the elevation of intermediate points on a site. This method involves
dividing the site into a grid of equal squares and then estimating the elevation
of the corners of each square to draw the contour lines.

Square Method

The following are
the steps involved in the square method of contour surveying:

Divide the site
into a grid of equal squares – The size of the squares will depend on the scale
of the map and the accuracy required. The squares can be drawn on the map or
photograph of the site.
Identify the
elevation of the corners of each square – The elevation of the corners of each
square can be estimated by using the contour lines on the map or photograph. The
elevation of the corner points can be estimated by interpolation based on the
known elevations of the contour lines. [ Surveying MCQ ]
Connect points of
equal elevation to draw contour lines – Once the elevation of the corner points
has been estimated, the contour lines can be drawn by connecting points of
equal elevation. The contour lines should be drawn at equal intervals, such as
1-foot, 2-feet, or 5-feet, depending on the requirements of the project.

The square method
of contour surveying is useful when direct measurement of elevation is not
possible or practical, such as in areas with dense vegetation or steep terrain.
However, this method has limitations and may not provide accurate results in
some cases. It is therefore important to verify the accuracy of the results by
comparing them with direct measurements or by conducting a ground survey.

It is important to
note that the square method of contour surveying is an indirect method and may
not be as accurate as direct methods of surveying such as the use of total stations
or GPS devices. The accuracy of the results will depend on the scale and
quality of the map or photograph used, as well as the skill and experience of
the surveyor in estimating elevations by interpolation. Therefore, it is
important to use this method with caution and to verify the results through
ground surveys or other direct methods of measurement.

Cross Sections Method

Indirect method of contouring in
cross section’s method

The indirect method
of contour surveying using the cross sections method is a technique used to estimate
the elevation of intermediate points along a cross section of the site. This
method involves drawing a cross section of the site and estimating the
elevation of specific points along the cross section to draw the contour lines.

Cross-Section Method

The following are
the steps involved in the cross-section’s method of contour surveying:

Draw a cross
section of the site – A cross section is a vertical slice of the site that shows
the elevation changes along a specific line. The cross section can be drawn by
hand or by using computer software. [ Equipment used in chain surveying ]
Identify the
elevation of specific points along the cross section – The elevation of specific
points along the cross section can be estimated by using the contour lines on
the map or photograph. The elevation of the points can be estimated by
interpolation based on the known elevations of the contour lines.
Connect points of
equal elevation to draw contour lines – Once the elevation of specific points
along the cross section has been estimated, the contour lines can be drawn by
connecting points of equal elevation. The contour lines should be drawn at
equal intervals, such as 1-foot, 2-feet, or 5-feet, depending on the
requirements of the project.

The cross sections
method of contour surveying is useful when direct measurement of elevation is
not possible or practical, such as in areas with dense vegetation or steep
terrain. However, this method has limitations and may not provide accurate
results in some cases. It is therefore important to verify the accuracy of the
results by comparing them with direct measurements or by conducting a ground
survey.

It is important to
note that the cross sections method of contour surveying is an indirect method and may not be as accurate as direct methods of surveying such as the use of
total stations or GPS devices. The accuracy of the results will depend on the
scale and quality of the map or photograph used, as well as the skill and
experience of the surveyor in estimating elevations by interpolation.
Therefore, it is important to use this method with caution and to verify the
results through ground surveys or other direct methods of measurement.

Tacheometric Method

Indirect method of contouring in
tacheometric method

The indirect method
of contour surveying using the tacheometric method is a technique used to
estimate the elevation of intermediate points on a site using a tacheometer. A
tacheometer is an instrument that is used to measure both the horizontal and
vertical angles between two points. This method involves measuring the
horizontal and vertical angles between two known points and then calculating
the elevation of intermediate points based on these measurements.

Tacheometric Method

The following are
the steps involved in the tacheometric method of contour surveying:

Set up the
tacheometer – The tacheometer should be set up at a point with a known
elevation, such as a benchmark or a point that has been surveyed using a direct
method. The tacheometer should be leveled and oriented to the north using a
compass.
Sight the target – The target is the point whose elevation needs to be estimated. The target
should be visible through the tacheometer telescope. [ Surveying MCQ ]
Measure the
horizontal and vertical angles – The tacheometer is used to measure the
horizontal and vertical angles between the known point and the target. The horizontal
angle is measured using the horizontal circle of the tacheometer, and the
vertical angle is measured using the vertical circle of the tacheometer.
Calculate the
elevation of the target – The elevation of the target can be calculated using
the measured horizontal and vertical angles, the distance between the known
point and the target, and the elevation of the known point. The elevation can
be calculated using the following formula: Elevation of target
= Elevation of known point + (Distance x tan (vertical angle) – height of
instrument) – (Distance x sin (horizontal angle) x sin (vertical angle))
Repeat the process
for other targets – The process can be repeated for other targets to estimate
their elevations and draw the contour lines.

The tacheometric
method of contour surveying is more accurate than the indirect methods using
the square method or cross sections method. However, it requires a tacheometer
and skilled operators, which may increase the cost of the survey. It is
important to verify the accuracy of the results by comparing them with direct
measurements or by conducting a ground survey.

Contour Map

A contour map, also
known as a topographic map, is a type of map that shows the elevation of the
land surface through contour lines. Contour lines are lines that connect points
of equal elevation on the land surface. The contour lines are drawn at regular
intervals, such as 1-foot, 2-feet, or 5-feet, depending on the requirements of
the project. In civil engineering, contour maps are used for a variety of
purposes, including land surveying, site planning, and infrastructure design.

The following are
some of the applications of contour maps in civil engineering:

Land surveying – Contour maps are commonly used in land surveying to determine the elevation and
slope of the land surface. Surveyors use the contour lines to estimate the
elevation of intermediate points on the site and to draw the contour lines on a
map or photograph.

Site planning – Contour maps are used in site planning to identify the natural features of the
land surface, such as hills, valleys, and water bodies. Site planners use the
contour lines to determine the best location for buildings, roads, and other
infrastructure to minimize the impact on the environment and to optimize the
use of the site.

Infrastructure
design – Contour maps are used in infrastructure design to determine the optimal
alignment and elevation of roads, bridges, pipelines, and other infrastructure.
Engineers use the contour lines to estimate the elevation changes along the
route and to design the infrastructure to minimize the impact on the
environment and to ensure the safety and efficiency of the infrastructure. [ Surveying Objective Question ]

Flood plain mapping – Contour maps are used in flood plain mapping to identify the areas that are
prone to flooding during heavy rainfall or other natural events. Floodplain
maps show the contour lines of the land surface, as well as the location of
rivers, lakes, and other water bodies, to help identify the areas that are at
risk of flooding.

Environmental
monitoring – Contour maps are used in environmental monitoring to track changes
in the elevation and shape of the land surface over time. Environmental
scientists use the contour maps to identify areas that are experiencing
erosion, subsidence, or other changes that may have an impact on the
environment.

In summary, contour
maps are an essential tool in civil engineering for land surveying, site
planning, infrastructure design, floodplain mapping, and environmental
monitoring. They provide a visual representation of the elevation and shape of
the land surface, which is critical for ensuring the safety, efficiency, and
sustainability of civil engineering projects.

Characteristics Of Contour Maps

The characteristics
of contour maps, also known as topographic maps, are determined by the purpose
for which they are created. However, there are some common characteristics that
are found in most contour maps. These characteristics include:

Contour lines – Contour lines are the primary characteristic of contour maps. They connect
points of equal elevation on the land surface and are drawn at regular
intervals, such as 1-foot, 2-feet, or 5-feet. The contour lines are typically
labeled with their elevation and are shown in brown colour.

Scale – Contour maps
have a scale that represents the ratio between the distance on the map and the
actual distance on the ground. The scale is usually expressed as a ratio, such
as 1:10,000 or 1 inch = 500 feet. The scale is essential for determining the
size and shape of the area covered by the map.

Legend – The legend
of the contour map provides a key to understanding the symbols, colours, and
other features on the map. The legend typically includes information about the
scale, contour interval, symbols used to represent landmarks, roads, water
bodies, and other features.

Coordinates – Contour maps include coordinates that indicate the location of the features on
the map. The coordinates can be expressed in different formats, such as
latitude and longitude, UTM (Universal Transverse Mercator) coordinates, or
state plane coordinates. [ Code signals of ranging ]

Orientation – The
orientation of the map is usually shown with a compass rose or a north arrow
that indicates the direction of north. This is important for identifying the
direction of features on the map and for orienting the map to the ground.

Relief – Contour
maps often show the relief or the vertical exaggeration of the land surface.
This is important for visualizing the three-dimensional shape of the land
surface and for understanding the steepness of the terrain.

Grid – The grid is a
network of lines that divides the map into equal sections. The grid is used for
locating features on the map and for measuring distances.

In summary, the
characteristics of contour maps include contour lines, scale, legend,
coordinates, orientation, relief, and grid. These characteristics provide the
essential information needed for understanding the elevation and shape of the
land surface and for designing civil engineering projects such as site planning
and infrastructure design.

FAQ’s

01. Method of contour surveying.

Direct Method

Indirect Method

02. What is contour surveying.

Contour surveying is a type of land surveying that involves mapping and measuring the elevation of the land surface to create contour lines on a topographic map.

03. What is Contour gradient.

Contour gradient refers to the rate of change of elevation along a contour line on a topographic map.

04. Indirect method of contour surveying.

The indirect method of contour surveying is a technique used to determine the contour lines of a piece of land when direct measurement of elevation is not possible or practical. This method involves the use of topographical maps and photographs to estimate the elevation of the land surface and to draw the contour lines.