Key Points
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: Topographic or Ordnance Survey Maps
- Topographical maps show the detailed surface features of the Earth and are also called topo-sheets or Ordnance Survey maps.
- The word topography comes from Greek words topos (place) and grapho (to draw).
- These maps are drawn on separate sheets, each showing a part of an area, which together give a complete picture.
- In India, topographical (Ordnance) maps are prepared by the Survey of India, Dehradun.
- Topographical maps show physical features using contours and man-made features using conventional symbols.
