Kerala State Syllabus 10th Standard Social Science Notes Chapter 4 Landscape Analysis through Maps
Finding the precise location of the earth’s surface features is essential for the preparation of maps. Every inch on earth is measured with the help of survey instruments and maps are prepared based on these measurements. The land survey of Indian subcontinent was completed under the leadership of English East India Company. These surveys were undertaken by Col. William Lambton over a period of 50 years. Col. George Everest joined as an assistant to Lambton in 1818. This was the first survey that recorded the correct measurements of the Himalayan mountain ranges. As a tribute to George Everest who took charge of the survey after Lambton, the highest peak in the Himalayan mountain range was given the name Mount Everest. The first topographic maps of the Indian subcontinent were prepared after the completion of the survey in 1854.
→ Topographic maps : The maps that depict in minute detail all natural as well as man made features on the earth’s surface.
→ Toposheets: Topographic maps are also known as toposheets.
→ Survey of India : The official agency respon-sible for the preparation of topographic maps in our country is the Survey of India with its head-quarters in Dehradun.
→ Map Series : The numbering of India’s toposheets are done on the basis of the India and Adjoining Countries Map Series. There are 105 sheets in this series, numbering from 1 to 105.
→ Million Sheets : The topographical maps made with the scale 1:1000000. The sheets cover 4° latitudinal and 4° longitudinal extent and are given numbers from 1 to 105. These numbers are known as Index numbers.
→ Degree Sheets : Topographic maps with 1° latitudinal and 1° longitudinal extent, prepared in 1:250000 scale.
→ Inch Sheets : Toposheets with 15′ (15 minutes) latitudinal and longitudinal extent, prepared in 1:50000 scale.
→ Contour lines : Imaginary lines drawn connecting places having the same elevation from the sea level.
→ Form lines : When it is difficult to measure the elevation of places through land surveys due to rugged terrain, the elevation is represented with the help of broken lines. These are form lines.
→ Spot height : Spot height represents the actual height of a place by recording the height in digits beside a black dot.
→ Triangulated height: Height of places estimated through trigonometric surveys are recorded in maps using’ A’ symbol.
→ Benchmark : The height of reservoirs and prominent buildings are recorded along with the letters BM.
→ Grid reference : The network of northings and eastings in the toposheets.
→ Contour interval : The difference between the value of two adjacent contours is called contour interval.
→ Intervisibility : If any two places in a topo-graphical map are mutually visible, then it can be said that these places have intervisibility.
→ Primary information: The general information given outside the margins in topographical maps are known as primary information.