Various features like mountains, hills, plateaus and plains are found on the earth’s surface. Elevations and depressions on the earth’s surface are known as the relief features of earth. Maps showing the relief features of earth are known as relief maps.
Many methods are used to show relief features on the maps. These methods include colour method, hachures, spot heights, bench marks, trigonometrical stations, hill shading, layer tints, contours, and form lines.
In colour method, different relief features are shown by different colours.
Hachures are fine broken lines drawn along the slopes of land.
Spot heights indicate the actual height of spots above the mean sea level.
Bench marks are placed on buildings, rivers, bridges, pillars, etc.
Trigonometrical stations are the points on the surface of earth used as stations for triangulation survey.
In hill shading method, the region shown in the map is illuminated by light, either vertically from above or from the north-west direction.
Layer tints are used to denote all the land between two contours.
Contours are the imaginary lines joining places having the same elevation above the mean sea level.
A map showing the landform of an area by contours is called a ‘contour map’.
The process of drawing contours with the help of heights of various points on the map is known as interpolation of contours.
Contour lines can be drawn by keeping in mind the characteristics of contours.
Various types of slopes that can be represented by contours are steep slope, gentle slope, uniform slope, concave slope, convex slope, terraced slope, and undulating slope. Contours representing steep slope are closely spaced. Contours representing gentle slope are far apart. Contours are evenly placed in uniform slope. Contours of the concave slopes are widely spaced in the lower parts and, closely spaced in the upper parts. Contours of the convex slopes are widely spaced in the upper parts and, closely spaced in the lower parts.
The various types of relief features that can be represented by contours on the map are conical hill, plateau, ridge, escarpment, V-shaped valley, spur, waterfall, and sea cliff.
A conical hill is represented by concentric contours spaced at almost regular intervals.
Contour lines representing a plateau are normally closely spaced at the margins.
The contours representing a ridge are elongated and closely spaced.
The contours representing an escarpment are very close but do not touch or cut each other.
Contour lines for the lowermost part of the V-shaped valley have very small gap between its two sides.
Spur is represented by V-shaped contours, but in a reverse manner.
Contours representing a waterfall merge into one another while crossing a river stream.
Contours in a sea cliff run very close to each other almost merging into one.
Form lines show only the approximate heights. They are used in place of contours where accurate survey is not possible due to complications in relief.