SanglapGeographer at 11:49, 3 April 2026

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{{short description|19th-century survey to measure the Indian subcontinent}}
{{Use British English|date=March 2018}}
{{Use dmy dates|date=August 2020}}
[[File:1922 Index of Great Trigonometrical Survey of India.jpg|thumb|upright=1.9|Index to the Great Trigonometrical Survey]]

The '''Great Trigonometrical Survey of India''' was a project that aimed to carry out a [[wikt:Special:Search/survey|survey]] across the [[Indian subcontinent]] with scientific precision. It was begun in 1802 by the [[British infantry]] officer [[William Lambton]], under the auspices of the [[East India Company]].<ref name="Gill">Gill, B. (2001); "The Big Man. Surveying Sir George Everest", in: ''Professional Surveyor Magazine'', Vol. 21 Nr 2. Retrieved [http://www.krcmar.ca/sites/default/files/2000_Winter_The%20Big%20Man-%20Surveying%20Sir%20George_1.pdf online] {{Webarchive|url=https://web.archive.org/web/20170210152803/http://www.krcmar.ca/sites/default/files/2000_Winter_The%20Big%20Man-%20Surveying%20Sir%20George_1.pdf |date=10 February 2017 }} 8 March 2016.</ref> Under the leadership of his successor, [[George Everest]], the project was made the responsibility of the [[Survey of India]]. Everest was succeeded by [[Andrew Scott Waugh]], and after 1861, the project was led by [[James Walker (Surveyor General)|James Walker]], who oversaw its completion in 1871.

Among the many accomplishments of the Survey were the demarcation of the [[United Kingdom of Great Britain and Ireland|British]] territories in the subcontinent and the measurement of the height of the [[Himalaya]]n giants: [[Mount Everest|Everest]], [[K2]], and [[Kangchenjunga]]. The Survey had an enormous scientific impact as well. It was responsible for one of the first accurate [[grade measurement|measurements]] of a section of an arc of [[longitude]], and for measurements of the [[Vertical deflection|geodesic anomaly]], which led to the development of the theories of [[isostasy]].

The native surveyors made use of in the Himalayas, especially in [[Tibet]] (where Europeans were not allowed), were called [[Pundit (explorer)|pundit]]s, who included the cousins [[Nain Singh Rawat]] and [[Kishen Singh Rawat]].<ref name=study4>Peter Hopkirk, 1982, "Trespassers on the Roof of the World: The Race for Lhasa", [[Oxford University]] Press.</ref><ref name="study9">Derek J. Waller, 2004, "[https://books.google.com/books?id=PYqWhpyoQsoC The Pundits: British Exploration of Tibet and Central Asia]," University Press of Kentucky.</ref><ref name=study1>Account of the Pundit's Journey in Great Tibet - Capt. H. Trotter, The Journal of the Royal Geographical Society (1877).</ref>

[[File:GTS Peninsula Asiatic Researches.jpg|thumb|upright=1.95|The first triangulations across the Peninsula]]

== 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.<ref name="Gill" /> 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 Presidency|Bengal]]. As Rennell proceeded to make maps, the lack of precise measurement was noticed.<ref name="Gill" /> 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 [[triangulation]]s, initially through the newly acquired territory of [[Kingdom of Mysore|Mysore]], and eventually across the entire [[subcontinent]].<ref>{{cite journal |title=An account of the Trigonometrical Operations in crossing the peninsula of India, and connecting Fort St. George with Mangalore |author=Lambton, William |pages=290–384 |url=https://archive.org/stream/asiaticresearche10asia#page/n307/mode/2up |journal=Asiatic Researches; or Transactions of the Society Instituted in Bengal for Inquiring into the History and Antiquities |year=1811}}</ref>
[[File:Calcutta Baseline 1832.jpg|thumb|upright=1.3|Measurement of the Calcutta baseline in 1832 based on a sketch by [[James Prinsep]]. This shows surveyors stretching a chain on coffers supported on pickets. The chain is housed under shade to reduce errors due to thermal expansion, and is aligned using a boning telescope.{{efn|A ''boning telescope'' was a small, low-magnification telescope used to align the survey markers.<ref>{{OED|bone, v.3}}</ref>}}]]
[[File:Ramsden_zenith_sector.jpg|thumb|left|upright|A [[zenith sector]] was an upward-facing telescope with accurate angle measurement scales. A star close to the zenith of known declination from the [[Polaris|Pole Star]] was used to determine latitude, as a direct measurement of the Pole Star could be affected by refraction.]]
The Great Trigonometrical Survey of India started on 10 April 1802 with the measurement of a baseline near [[Chennai|Madras]].<ref name="Gill" /> Major Lambton selected the flat plains with [[St. Thomas Mount]] at the north end and Perumbauk Hill at the southern end. The baseline was {{convert|7.5|mi|km}} long. Lieutenant Kater was dispatched to find high vantage points on the hills of the west so that the coastal points of [[Thalassery|Tellicherry]] and [[Kannur|Cannanore]] could be connected. The high hills chosen were [[Ezhimala Hill|Mount Delly]] and [[Tadiandamol]]. The distance from coast to coast was {{convert|360|mi|km}}, and this survey line was completed in 1806.<ref name=markham>{{cite book |first=Clements |last=Markham |author-link=Clements Markham |title=A Memoir on the Indian Surveys |url=https://archive.org/details/memoirontheindia025502mbp |year=1878 |publisher=London. W H Allen And Co. |edition=2 |access-date=2009-03-01 |page=[https://archive.org/details/memoirontheindia025502mbp/page/n98 67]}}</ref> 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 [[Triangulation|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.<ref name="Gill" /> At times the survey party numbered 700 people.<ref>''Bluesci: Cambridge university science magazine'', 29 January 2011,"History: The Great Trigonometrical Survey" {{Cite web |url=http://www.bluesci.org/?p=2028- |title=BlueSci » History: The Great Trigonometrical Survey |access-date=5 May 2013 |archive-date=27 July 2014 |archive-url=https://web.archive.org/web/20140727125305/http://www.bluesci.org/?p=2028- |url-status=dead}}, Cambridge.</ref>
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.<ref>{{cite book |pages=39–40 |title=A memoir of the Indian Surveys, 1875–1890 |author=Black, Charles E.D. |year=1891 |place=London |publisher=Secretary of State for India in Council |url=https://archive.org/stream/memoironindiansu00blac#page/39/mode/1up}}</ref>[[File:Survey_towers_GTS.jpg|thumb|upright=1.05|Survey towers used by [[George Everest]] to elevate the instruments]]

== Instruments and methods used ==
Triangulation surveys were based on a few carefully measured baselines and a series of angles. The initial baseline was measured with great care since the accuracy of the subsequent survey was critically dependent upon it. Various corrections were applied, principally temperature. An especially accurate [[folding chain]] was used, laid on horizontal tables, all shaded from the sun and with constant tension. The early surveys made use of large and bulky [[theodolite]]s made by William Carey,<ref>{{Cite magazine |last=R. |first=Ramachandran |date=2021-06-02 |orig-date=Originally appeared in print version on 27 April 2002 |title=Survey Saga |url=https://frontline.thehindu.com/the-nation/survey-saga/article30244732.ece |access-date=2022-12-26 |magazine=Frontline |language=en}}</ref> a [[zenith sector]] made by [[Jesse Ramsden]], and {{convert|100|ft|m|adj=on}} chains. Later surveys used more compact theodolites.
[[File:Great Trigonometrical Survey Tower - Sukchar - North 24 Parganas 2012-04-11 9482.JPG|thumb|upright=1.05|One of the survey towers in [[Kolkata]] in 2012]]
Accurate instruments could not always be purchased through the standard system of government contract, and Everest personally supervised the construction of instruments. He had a maker, Henry Barrow, set up an instrument company in Calcutta. Barrow was succeeded by Syed Mohsin from [[Arcot, Tamil Nadu]], and after his death, the instruments were supplied by Cooke from [[York]].<ref name=strahan>{{cite journal |author=Strahan, C. |year=1903 |title=The Survey of India |url=https://archive.org/stream/professionalpape28grea#page/n211/mode/2up |journal=Professional Papers of the Corps of Royal Engineers |volume=28 |pages=141–171}}</ref><ref>{{cite journal |url=http://www.new1.dli.ernet.in/data1/upload/insa/INSA_1/20005abc_47.pdf |author=Insley, Jane |journal=Indian Journal of History of Science |volume=30 |issue=1 |year=1995 |title=Making mountains out of molehills? George Everest and Henry Barry, 1830–39 |pages=47–55 |url-status=dead |archive-url=https://web.archive.org/web/20140125144649/http://www.new1.dli.ernet.in/data1/upload/insa/INSA_1/20005abc_47.pdf |archive-date=25 January 2014}}</ref>

=== Correcting deviations ===
To achieve the highest accuracy, a number of corrections were applied to all distances calculated from simple trigonometry:
* [[Curvature of the Earth]]
* The non-spherical nature of the curvature of the Earth
* [[Gravitation]]al influence of mountains on [[pendulum]]s and plumb lines<ref>{{cite journal |title=On the Attraction of the Himalaya Mountains, and of the Elevated Regions beyond Them, upon the Plumb-Line in India |first=John Henry |last=Pratt |journal=Philosophical Transactions of the Royal Society of London |volume=145 |year=1855 |pages=53–100 |jstor=108510 |doi=10.1098/rstl.1855.0002 |url=https://zenodo.org/record/1432414 |doi-access=free}}</ref>
* [[Atmospheric refraction#Terrestrial refraction|Refraction]]
* [[Height above mean sea level]]

== Superintendents ==
*1818–1823 – [[William Lambton]]
*1823–1843 – [[George Everest|Sir George Everest]]
*1843–1861 – [[Andrew Scott Waugh]]
*1861–1883 – [[James Walker (Surveyor General)|James Thomas Walker]]
*1884–1888 – [[Charles Thomas Haig]]
*1888–1894 – [[George Strahan (engineer)|George Strahan]]
*1894–1899 – [[St George Corbet Gore]]
*1899–1911 – [[Sidney Gerald Burrard]]
*1912–1921 – [[Gerald Lenox-Conyngham|Sir Gerald Ponsonby Lenox-Conyngham]]

== See also ==
* [[Principal Triangulation of Great Britain]]

==Notes==
{{notelist}}
{{Clear}}

== References ==
{{reflist}}

== Further reading ==
{{commons category}}
* {{cite book |last=Edney |first=Matthew H. |title=Mapping an Empire: The Geographical Construction of British India, 1765-1843 |url=https://books.google.com/books?id=LF_FBgAAQBAJ |year=2009 |publisher=University of Chicago Press |isbn=978-0-226-18486-9}}
* [[John Keay]]. 2000. ''[https://books.google.com/books?id=JgsgAQAAIAAJ The Great Arc]'', London: HarperCollins. {{ISBN|0-00-257062-9}}.
* {{Cite book |last=Dean |first=Riaz |title=Mapping The Great Game: Explorers, Spies & Maps in Nineteenth-century Asia |publisher=Casemate (UK) |year=2019 |isbn=978-1-61200-814-1 |location=Oxford |pages=67–123 |url=https://books.google.com/books?id=WF3JDwAAQBAJ}}
* {{citation |title=The Great Trigonometrical Survey of India in a Historical Perspective |first=Rama |last=Deb Roy |journal=Indian Journal of History of Science |volume=21 |number=1 |pages=22–32 |year=1986 |url=http://www.new1.dli.ernet.in/data1/upload/insa/INSA_1/20005b5b_22.pdf |archive-url=https://web.archive.org/web/20140125140928/http://www.new1.dli.ernet.in/data1/upload/insa/INSA_1/20005b5b_22.pdf |archive-date=25 January 2014}}
* Reginald Henry Phillimore, ''Historical Records of the Survey of India,'' 5 vols. Dehra Dun, Survey of India (1945–1968)
** [https://archive.org/details/in.gov.ignca.35328 Volume 1: 18th Century]; [https://archive.org/details/in.gov.ignca.35329 Volume 2: 1800 to 1815]; [https://archive.org/details/in.gov.ignca.27830 Volume 3: 1815 to 1830]; [https://archive.org/details/in.gov.ignca.27831 Volume 4: 1830 to 1843]; [https://archive.org/details/1968-historical-records-of-survey-of-india-vol-5-by-phillimore-s-volume-v Volume 5: 1844 to 1861]

[[Category:1802 establishments in British India]]
[[Category:Cartography by country|India]]
[[Category:Geodetic surveys]]
[[Category:Historical geography of India]]
[[Category:Surveying of India]]
[[Category:1871 disestablishments in Asia]]
[[Category:19th century in British India]]

Great Trigonometrical Survey - Revision history

SanglapGeographer at 11:49, 3 April 2026