Originally set up in 1767, the Survey of India is the government's oldest department and in charge of all of the its mapping and surveying efforts. Since coordinating the Great Trigonometric Survey, it has expanded over the years to 23 geospatial data centers and 18 divisions that range in responsibilities from tides to aerial survey. The agency uses GIS extensively in its mapping activities.
The Great Arc (ISBN 0-00-257062-9) by John Keay details the challenges in completing the Survey of India's Great Trigonometric Survey or Great Arc, an epic project that both carefully mapped the country and measured the curvature of the earth.
Begun in 1800 by William Lambton, an English army captain, and completed by his assistant George Everest, for whom the famous Himalayan Mountain was named, the project stretched for nearly 50 years and 1,600 miles.
The survey process was based on triangulation, a method in which a baseline is accurately measured and the angles of the desired triangle are calculated by sighting a point with a theodolite, an instrument used to measure both horizontal and vertical angles. One side of the calculated measurements of the first triangle is then used as the base line for the next triangle and so on. The end result was a triangulation network of varying sizes that progressively moved towards the Himalayas.
This procedure is complicated because the earth is uneven and shaped like an oblate spheroid. This means that the angles of the calculated triangles did not add up to 180 degrees and spherical excess had to be calculated and removed.

Lambton's Great Theodolite used by both William Lambton and George Everest during the Great Trigonometric Survey of India was capable of measuring both the vertical and horizontal access, it weighed approximately half a ton and needed twelve men to carry it. This image was taken from the 'Historical Records of the Survey of India 1830 to 1843', Volume IX plate 6.
