Great Trigonometrical Survey

The Great Trigonometrical Survey was a 19th-century British project that measured the Indian subcontinent through triangulation and established heights for Himalayan peaks.

Triangulation: A surveying method that determines locations by measuring angles in a network of triangles from a known baseline. The survey extended measured baselines into a continental network of triangles.
William Lambton: A British surveyor who initiated the Great Trigonometrical Survey in southern India in 1802. Lambton began the project and directed its early triangulation.
Mount Everest: The world’s highest mountain above sea level, in the Himalayas on the Nepal–China border. The survey calculated the height of Peak XV, later named Mount Everest.
Kalianpur: A village in central India used as a key reference point in the triangulation network of the Great Trigonometrical Survey. Its adopted coordinates served as a central geodetic reference for mapping India.
Baseline measurement: The precise measurement of a short reference distance used to scale a larger triangulation network. Accurate baselines anchored the survey’s much larger network.
George Everest: A British surveyor who led the Great Trigonometrical Survey from 1823 to 1843. Everest extended and reorganized the survey after Lambton’s death.
Himalayas: A mountain range in Asia, stretching across several countries and containing the world’s highest peaks. The survey’s best-known peak calculations concerned this mountain range.
Peak XV: The survey designation for the Himalayan mountain later named Mount Everest. Its height was calculated from observations made at great distances.
Theodolite: An instrument for measuring horizontal and vertical angles, used in surveying and geodesy. Survey teams used large theodolites to observe angles between distant stations.
Survey of India: India’s national mapping agency, established in 1767 and responsible for topographic and geodetic surveys. The Great Trigonometrical Survey became a central undertaking of this institution.

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