Great Trigonometrical Survey

Among the many accomplishments of the Survey were the demarcation of the British territories in the subcontinent and the measurement of the height of the Himalayan giants: Everest, K2, and Kangchenjunga. The Survey had an enormous scientific impact as well. It was responsible for one of the first accurate measurements of a section of an arc of longitude, and for measurements of the geodesic anomaly, which led to the development of the theories of isostasy.

The native surveyors employed in the Himalayas, especially in Tibet (where Europeans were not allowed), were called pundits, and included the cousins Nain Singh Rawat and Kishen Singh Rawat.

History

From its inception in 1600 to its domination of the entire Indian subcontinent by the beginning of the nineteenth century, the British East India Company gained more and more territory. With the acquisition of new territory, it employed several explorers and cartographers to provide maps and other information on its territories, most notably James Rennell, from 1767 in Bengal. As Rennell proceeded to make maps, the lack of precise measurement was noticed. In 1800, shortly after the Company victory over Tipu Sultan, William Lambton, an infantry soldier with experience in surveying, proposed to remedy precisely that, through a series of triangulations, initially through the newly acquired territory of Mysore, and eventually across the entire subcontinent.

The Great Trigonometrical Survey of India started on 10 April 1802 with the measurement of a baseline near Madras. Major Lambton selected the flat plains with St. Thomas Mount at the north end and Perumbauk Hill at the southern end. The baseline was 7.5 miles (12.1 km) long. Lieutenant Kater was dispatched to find high vantage points on the hills of the west so that the coastal points of Tellicherry and Cannanore could be connected. The high hills chosen were Mount Delly and Tadiandamol. The distance from coast to coast was 360 miles (580 km), and this survey line was completed in 1806. The East India Company thought that this project would take about five years, but it took nearly 70 years, well past the Indian Rebellion of 1857 and the end of company rule in India. Because of the extent of the land to be surveyed, the surveyors did not triangulate the whole of India but instead created what they called a "gridiron" of triangulation chains running from north to south and east to west. At times the survey party numbered 700 people.

The Trigonometrical Survey was conducted independently of other surveys, notably the topographical and revenue surveys. In 1875, the decision was taken that the Survey budget should be reduced from 240,000 to 200,000 pounds. This resulted in a reorganization under Surveyor-General Colonel J.T. Walker to amalgamate the Great Trigonometrical, Topographical and Revenue Surveys into the Survey of India.