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Contour Mapping With Contour Lines

A contour line can also be called an isoline, isopleth, or isarithm. The lines are the function of two variables, a curve. Here the function has a constant value, here the curve joins the points of an equal value. Contour lines are plane sections of the dimensional graph.

In cartography, a contour line is normally called a ‘contour’. These lines join points having equal elevated heights, above a predetermined level, normally the sea level. 

These contour lines often illustrate a contour map, which is the main topic of discussion in this specific content. For example, a topographic map, showing valleys and hills, its steepness or gentleness of the slopes is represented by the contour lines. We will vividly discuss Contour Mapping in our subsequent sections. 

Contour Mapping

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First and foremost, we will answer ‘what is a contour map?’ 

A contour map is a type of map where the shape of the land surface is shown by the contour lines, the relative spacing done between these lines indicates the relative slope of the particular surface.

Contour map meaning is quite clear to us, if we further deduce this definition it means – this is the delineation of any property in the map which is formed by constructing lines. The lines are carved based on the equal values of that property which is available as data points. 

In the contour map meaning, it can be said that contour mapping is a type of topography mapping, but to distinctly study the concept we will find there is an acute difference between the two, so we cannot use each other as synonyms. A topographic map is an accurate map that displays natural terrain and also man-made objects like buildings, roads, or bridges. While Contour maps represent changes in the elevation with the help of contour lines. 

Each of the contour lines being marked on a map joins the points having an equal height. The method of contouring cannot be totally relied on because two investigators can produce different types of maps whenever interpolation between two data takes place. 

Contour Mapping According to the Crustal Thickness

A contour map of global having the crustal thickness represents the bimodal division of the earth's crustal thickness. The ocean basins have 6 to 7 km thick crust (excluding 4 to 5 km of water). The continents have an average thickness measuring 39.7 km. The crust is generally 30 km measured for thickness in the ocean-continent margin and this gradually increases towards the continental interior towards 40 to 45 km. The crust which is thicker than 50 km is only to few regions, which includes the Tibetan Plateau located in western China, the Andes in western South America. The contour map shows merely the large-scale crustal features, hence the regions with locally thick crust are not visible in this map. The crust does not display the pattern of increased thickness with the increase in age, as this would be the case if the same were to be repeatedly subjected to the igneous intrusions which are from the underlying mantle. For example, the crust located in western Australia is older compared to that in central Australia, yet the crust is a minimum of 10 km thinner in western Australia. This crust has a thickness which is in excess of 50 km, this is almost a young and active mountain belt. These regions consist of high topography and are vulnerable to rapid erosion. 

Contours Geography 

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What is a Contour?

Contours are imaginary lines. These lines connect points of the same value. A contour map generally shows different contours such as the elevation or even the temperature contours.

Contours are the lines on a map that join the same height. The Contour interval refers to the variation in height, example the contours are drawn at every meter. 

 Contour lines on a map basically illustrate the height of a distinct place. This also helps us to obtain information regarding the steepness of the slopes, which is along the direction of the land that is sloping.

The contours here form patterns representing how steep the slopes actually are. The closer the contour lines are stuck together; the steeper is the slope.

With this result, we can study the relief of the land; whether this is a valley, a mountain, a valley which has a flat floor, also we can study if the valley has a stream, or not, or is it around the cone-shaped hill or a hilltop.

Uses of Contour Mapping

The Contours provide important information which can help us to study the nature of the terrain. This proves to be useful for the selection of sites, to determine the catchment area of a drainage basin, or to find intervisibility between two or more stations, etc. Some of the uses of contours are described below.

Nature of Ground

To study the nature of the ground which catches interest.

To Locate Route

To identify the route, a contour map provides worthy information on how to locate a route.

Intervisibility Between Stations

When the intervisibility between the two points cannot be easily ascertained by inspecting the area, then the contour map comes to the rescue. 


To Determine Catchment Area or Drainage Area

The catchment area of a particular river can be well determined by using the contour map. The watershed line very well indicates the drainage basin of the river which passes through the ridges and then saddles of the terrain that turns around the river. It is always perpendicular to the contour lines. The catchment area which is contained between this watershed line and the river outlet is measured with a planimeter.

FAQs (Frequently Asked Questions)

1. What Do You Mean By Igneous Intrusion?

Ans. Igneous intrusions occur when the magma from the volcano cools and it solidifies before this reaches the earth’s surface. Three common types of such intrusion are dykes, sills, and batholiths.

Sometimes the magma forces itself through a crack or through a fault in the rock at the Earth's surface. This magma is poured out over the Earth's surface in a volcanic eruption. This process is known as extrusion. The rocks which are formed from these extruded magmas are called extrusive igneous rocks. Example -Basalt and pumice are formed through the process of extrusive igneous rocks.

2. Can the Contour Maps Determine the Storage Capacity of a Reservoir?

Ans. The storage capacity of a reservoir is well determined from the contour map. The contour lines marked in the contour map indicate the full reservoir level (abbreviated as F.R.L), this is drawn on the contour map. The area which is enclosed between the successive contours is measured by a planimeter. While the volume of water which is between the F.R.L and the river bed is estimated.

3. What is a Planimeter?

Ans. The planimeter is a drafting instrument, this helps in measuring the area of the planar region. This region being measured can have an irregular shape which makes the instrument versatile.

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