- Relief refers to the height, slope, and shape of land such as mountains, plains, and plateaus.
- Landforms have three dimensions—length, breadth, and height.
- Maps are two-dimensional, showing only length and breadth.
- Special methods are used to show height and slope on maps.
- The main methods of relief representation are hachures, hill shading, form-lines, and contours.
Key Points
Key Points: Representation of Relief Features
Key Points: Methods of Representation of Relief on the Map > Contours
- Contours are imaginary lines joining places of the same height above mean sea level (MSL) and show height, slope, and relief.
- Contour interval is the vertical distance between two consecutive contours; in ICSE topographical maps it is 20 metres.
- Index contours are every fifth contour line and are thicker and numbered, while intermediate contours are not numbered.
- Contours are continuous lines that never break or intersect, though they may merge in case of steep slopes or cliffs.
- Spacing and shape of contours help identify slopes and features: close lines show steep slopes, wide lines show gentle slopes, and V-shaped contours indicate river valleys.
Key Points: Identification of Landforms Marked by Contours
- Contour spacing shows slope: close lines = steep slope, wide lines = gentle slope, merging lines = cliff.
- Circular contours indicate hills or plateaus; contour values increase inward.
- V-shaped contours show valleys and spurs; in valleys, values decrease towards the centre.
- Special landforms such as ridges, passes, plateaus, dunes, depressions, and watersheds are identified by their contour patterns.
- Heights on maps are shown by triangulated heights (△), spot heights (•), bench marks (BM), and relative height (r).
Key Points: Conventional Signs and Symbols used in Topographical Maps
- Conventional signs and symbols are standard signs used to show features on topographical maps.
- Colours have fixed meanings: red–man-made, blue–water, green–vegetation, yellow–cultivation, brown–relief, black–names and boundaries.
- Buildings and settlements are shown by specific symbols such as huts, temples, mosques, churches, and tombs.
- Transport features like roads, railways, bridges, passes, and causeways have separate symbols.
- Important facilities such as post offices, hospitals, police stations, power lines, and quarries are shown using symbols.
Important Questions [3]
- Study the extract of the Survey of India Map sheet No. G43S7 and answer the following question: What is the contour interval used in the given map extract?
- Study the extract of the Survey of India Map sheet No. G43S7 and answer the following question: What do you understand by .10r in 2709?
- Study the extract of the Survey of India Map sheet No. G43S7 and answer the following question: What is the pattern of drainage seen in the grid square 2505?
