Mapping And Contouring

Contouring

What is Contouring:

Contouring is the science of representing the vertical dimension of the terrain on a two dimensional map.

Characteristics of Contours:

Contours show distinct characteristic features of the terrain as follows:

i) All points on a contour line are of the same elevation.
ii) No two contour lines can meet or cross each other except in the rare case of an overhanging vertical cliff or wall
iii) Closely spaced contour lines indicate steep slope
iv) Widely spaced contour lines indicate gentle slope
v) Equally spaced contour lines indicate uniform slope
vi) Closed contour lines with higher elevation towards the centre indicate hills
vii) Closed contour lines with reducing levels towards the centre indicate pond or other depression.
viii) Contour lines of ridge show higher elevation within the loop of the contours. Contour lines cross ridge at right angles.
ix) Contour lines of valley show reducing elevation within the loop of the contours. Contour lines cross valley at right angles.
x) All contour lines must close either within the map boundary or outside.

Uses of Contour maps:

Contour maps are extremely useful for various engineering works:

1. 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.
2. 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.
3. Inter-visibility of any two points can be found by drawing profile of the ground along that line.
4. The routes of the railway, road, canal or sewer lines can be decided so as to minimize and balance earthworks.
5. 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.
6. From the contours, it is possible to determine the capacity of a reservoir.

Mapping

What is Mapping:

•  A map is a graphic form, normally to scale, of spatial abstraction of features on, or in relation to, the surface of the Earth.
• A Graphic organizer that shows relationships among connected concepts and ideas.

 Types of maps:

1. Topographic map: A reference tool, showing the outlines of selected natural and man-made features of the Earth. ? "Topography" refers to the shape of the surface, represented by contours and/or shading, but topographic maps also show roads and other prominent features.

2. Thematic map: A tool to communicate geographical concepts such as
 - The distribution of population densities, climate, movement of goods, land use etc
 - Line maps versus photo (image) map
 - 2D vs 3D maps 

Characteristics of maps:

1. Scale: The scale of a map is the ratio between distances on the map and corresponding distances in the real world, e.g., if a map has a scale of 1:50,000, then 1 cm on the map equals 50,000 cm or 0.5 km on the Earth's surface. "Small scale" and "large scale" is often confused, e.g, 1:50,000 vs. 1:500,000
2. Projection:  A projection is a method by which the curved surface of the earth is represented on a flat surface.Numerous projections have been invented for various applications