Index chart to the Great Trigonometrical Survey of India, 1870.

In 1799 Colonel William Lambton proposed a plan for a mathematical and geographical survey. The main aims of what later became the Great Trigonometrical Survey of India were to determine the location of geographical features in terms of latitude and longitude, and to calculate the size of the Earth, using the arc of meridian as a gauge for Earth's diameter. George Everest (1790-1866) worked on the Survey between 1818 and 1843, and was appointed Surveyor General in 1830. The Survey was the longest arc of the meridian ever surveyed. It began at Cape Comorin in 1806, and covered a distance of almost 2400 kilometers, reaching as far north as the Himalayas. It was finally completed in 1866.