Topographical maps and sheets

Topographical maps, also called general purpose maps, are drawn at large scales and show natural and cultural features: relief, vegetation, water bodies, cultivated land, settlements and transport. Geographers use them as base maps for drawing all other maps.

• Each country's national mapping organisation makes them; in India, the Survey of India.
• They come in series: every map in a series uses the same reference point, scale, projection, conventional signs, symbols and colours.
• Relief is shown mainly by contours and spot heights.

Two series:

• The India and Adjacent Countries Series was made until the Delhi Survey Conference of 1937. After that, the Survey of India stopped mapping neighbouring countries and mapped India to the specifications of the International Map Series of the World, but kept the old numbering system and layout.
• The International Map Series produces standard maps for the whole world at 1 : 10,00,000 and 1 : 250,000.

Scales and coverage of India's topographical sheets:

• 1 : 10,00,000: 4° × 4°
• 1 : 250,000: 1° × 1°
• 1 : 1,25,000: 30' × 30'
• 1 : 50,000: 15' × 15'
• 1 : 25,000: 5' × 7'30"

Reading a sheet. Learn the legend, the conventional signs and the colours. Because these signs are internationally accepted, a map can be read anywhere without knowing the local language. On Survey of India sheets, yellow shows cultivated land, green forest, blue water features, brown contours, and red and black roads, settlements and other man-made features.

Ways of showing relief: hachures (short lines along the steepest slope), hill shading, layer tints, bench marks and spot heights, and contours. Contours and spot heights are the main ones on topographical sheets.

Example (new): a district planner who needs to choose a site for a new school can start from a 1 : 50,000 sheet, which already shows the roads, villages, streams and slopes of the area on one page.