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8/3/2019 Basics of Contours
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Lecture on
Basics Characteristics of Contour
Lines
by
RAAJ RamsankaranBITS Pilani
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Contour lines
Contour lines are a method of depicting the 3-dimensional
character of the terrain on a 2-dimensional map.
Understanding contours is a very useful navigation skill
because you can identify the lay of the land and landscape
features as they appear on the ground.
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View of contours in 3D and 2D
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Steep slopes - contours are closely spaced
Gentle slopes - contours are less closely spaced
Valleys - contours form a V-shape pointing up the hill - these
V's are always an indication of a drainage path which could
also be a stream or river.
Ridges - contours form a V-shape pointing down the hill
Summits - contours forming circles
Depressions - are indicated by circular contour with lines
radiating to the center
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Why do you need to know the
terrain features on a map?
In order to locate a point on a map
In order to navigate from one point to the next
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Types of Terrain Features
Major-Five
Minor-Three
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Identification of Terrain Features
using Hand
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Five Major Terrain Features
Hill
Ridge
Valley
Saddle
Depression
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Hill
A hill is a point or small area of high ground. When you are on a hilltop, theground slopes down in all directions. The height and slope of a hill are
represented on a map by the number of concentric contour rings and the
distance between the rings.
Major
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Ridge
A ridge is a line of high
ground with height variations
along its crest. A ridge is not
simply a line of hills. All of the
points of the ridge crest arehigher than the ground on
both sides of the ridge. You
can identify a ridge on a map
by looking for contour lines
forming a U or V. The closedend of the U or V points away
from high ground.
Major
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Valley
A valley is a reasonably
level ground bordered on thesides by higher ground. It
generally has room to
maneuver within it. A valley
may or may not contain a
stream course running
through it. Contour lines
indicating a valley are U-
shaped and are usually a
dotted or broken line.
Arrows that point
upstream are valleys
MajorMajor
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What terrain feature is represented by contour
lines that tend to parallel a stream before crossing
and form a U?
VALLEYVALLEY
What terrain feature is represented by contourWhat terrain feature is represented by contourlines forming concentric circles?lines forming concentric circles?
HILLHILL
What terrain feature is a line of high ground withWhat terrain feature is a line of high ground with
height variations along its crest?height variations along its crest?
RIDGERIDGE
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Saddle
A saddle is a dip or low
point along the crest of a
ridge. A saddle is not
necessarily the lower ground
between two hilltops. It may
also be a break along anotherwise level ridge crest. A
saddle is normally represented
as an hourglass shape on a
map. The hourglass is made
by contour lines narrowing
between two groups of
concentric circles that indicate
hilltops or points of raised
ground.
MajorMajor
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Depression
A depression is a low point
or hole in the ground that is
also surrounded on all sides
by higher ground. A
depression generally has noor little room to maneuver
within it. The map symbol
that represents a depression
is closed contour lines that
have tick marks. The tickmarks point toward the low
ground or down slope
MajorMajor
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HillHill DepressionDepression RidgeRidge
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ValleyValley SaddleSaddle
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Two Minor Terrain Features
Draw
Spur
Cliff
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Draw
A draw is similar to a valley except itA draw is similar to a valley except it
usually has a less developed course.usually has a less developed course.
There is generally no level groundThere is generally no level ground
and, therefore, little or no room toand, therefore, little or no room to
maneuver. The ground slopes upwardmaneuver. The ground slopes upward
on each side and toward the head ofon each side and toward the head of
the draw. Draws are caused by flashthe draw. Draws are caused by flash
floods and can be found on flat terrainfloods and can be found on flat terrain
but are more often found along thebut are more often found along the
sides of ridges. Contour linessides of ridges. Contour lines
indicating a draw are shaped like a Vindicating a draw are shaped like a Vwith the point of the V pointingwith the point of the V pointing
toward the head of the draw. Thattoward the head of the draw. That
means the point is pointing toward themeans the point is pointing toward the
high ground.high ground.MinorMinor
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Spur
A spur is usually a short,A spur is usually a short,
continuously sloping line ofcontinuously sloping line of
higher ground, normallyhigher ground, normally
jutting out from the side ofjutting out from the side ofa ridge. A spur is oftena ridge. A spur is often
formed by two very parallelformed by two very parallel
streams cutting gullies orstreams cutting gullies or
draws down the side of adraws down the side of a
ridge. You can spot a spurridge. You can spot a spur
on a map when the contouron a map when the contour
lines form a U or V shapelines form a U or V shape
that points away from thethat points away from the
higher ground.higher ground.
MinorMinor
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CliffA cliff is a vertical or nearA cliff is a vertical or near--vertical slope. A cliff may be shownvertical slope. A cliff may be shown
on a map by contour lines that are very close together. A cliff ison a map by contour lines that are very close together. A cliff isalso shown as a ticked contour line with the tick marksalso shown as a ticked contour line with the tick marks
pointing towards the lower ground.pointing towards the lower ground.
MinorMinor
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What terrain feature is a vertical or near vertical
slope?
CLIFF
What terrain feature is represented by contour lines
are V-shaped with the point of the V toward the headof the high ground?
DRAW
What terrain feature is represented by short,
continuously sloping line of higher ground jutting out
the side of a ridge?
SPUR
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CliffCliff DrawDraw SpurSpur
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Contour Lines and Valleys
ContoursContours
Contours wrapped in 3D viewContours wrapped in 3D view
Source: Stephen J. Reynolds and Carla McAuliffe, Arizona State University
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Methods of Contouring
Direct Methods
Indirect Methods
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Direct Methods
In the direct method, the contour to be plotted is actually
traced on the ground. Points which happen to fall on adesired contour are only surveyed, plotted and finally
joined to obtain the particular contour. This method is
slow and tedious and thus used for large scale maps, small
contour interval and at high degree of precision.
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Indirect Methods
In this method, the spot levels of selected guide points are
taken with a level and their levels are computed. Thehorizontal positions of these points are measured or
computed and the points are plotted on the plan. The
contours are then drawn by a process called interpolation of
contours from the levels of the guide points. The following
are the indirect methods are commonly used for locating
contours.
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Different Indirect Methods
SquaresSquares oror GridGrid methodmethod
Cross section method
Tacheometric method
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Sources of Information
http://www.outdoored.com/Articles/Article.aspx?ArticleID=111
http://www.armystudyguide.com/content/army_board_study_guide_topics/land_navigation_map_reading/identify-major-minor-
terr.shtml