One of the great scientific questions of the 18th and 19th centuries was the accurate determination of the dimension of the Earth, and the subsequent location of geographical features in terms of latitude and longitude. Surveyors pursued the answer to this question with great zeal.
One of the most important initiatives was the measurement of an arc of meridian from Tinavelley, at the southern tip of India, to Banog, in the foothills of the Himalayas. At the time, the work was justified as part of an attempt to provide an accurate base for systematic topographic and revenue surveys, but it was also part of an attempt to answer one of the thorniest scientific problems of the day.
One of the most important initiatives was the measurement of an arc of meridian from Tinavelley, at the southern tip of India, to Banog, in the foothills of the Himalayas. At the time, the work was justified as part of an attempt to provide an accurate base for systematic topographic and revenue surveys, but it was also part of an attempt to answer one of the thorniest scientific problems of the day.
The Great Trigonometric Survey was an attempt to measure an arc of 78¡E from Tinavelley to Banog.
The objective was to determine the size of the Earth. The story begins with the Greek scholar Eratosthenes. Around 250 bc, he computed the arc distance between Alexandria and Syrene in Egypt by comparing the altitude of the noon sun during a summer solstice in both places. He measured the arc distance between the two cities as 7'12", which is 1/50th of the circumference of the Earth. Based on an estimate of the distance between the two cities, he estimated the circumference of the Earth as 46,250 km, which is only 15% larger than the presently accepted value. After Eratosthenes, the search stalled, and it was only in the 18th century that attempts were once again made to use the arc of meridian as a gauge for the diameter of the Earth. Some attempts are listed in Table 1.
Attempts to compute distance from an arc of meridian led naturally to the idea of providing accurate positions measured in latitude and longitude. This position could then be transferred to many other points by means of triangulation. William Roy and Michael Topping, in the 18th century, were two of the early advocates of triangulation. Roy is remembered today for a survey that linked the royal observatories of Greenwich and Paris. General Watson first conceived the idea of a trigonometrical survey in 1745.
In India, momentum grew. In 1784 Alexander Dalrymple suggested a triangulation along the eastern coast of India. Fortuitously, Topping was appointed Marine Surveyor in 1791. Between 1790 and 1791, Reuben Burrow's attempted to measure an arc in Bengal. In 1799, Col. William Lambton proposed a plan of a Mathematical and Geographical Survey right across the subcontinent.
In his proposal, Lambton noted: the surveyors of particular districts will be spared much labour when they know the position of some leading points to which they can refer because, when these points are laid down in the exact situations in which they are upon the globe, all the other objects will also have their situations true in latitude and longitude.
The proposal also included measurement of the meridional arc along 78û E, which passes just to the east of Cape Comorin, the southernmost tip of India, in order to determine the size of the Earth. Government approval was given in February 1800. In September 1800, Lambton did a trial survey of a base line near Bangalore.
The trigonometrical survey commenced on 10 April 1802, with the measurement of a base line near Madras. The baseline was 12.8 km long on a flat plain, with St Thomas Mount near its northern end and Perambalur hill near the southern end. From the Madras base line, a series of triangles was carried up to the Mysore plateau; a second base was measured near Bangalore, in 1804, by Lt. Warren.
The series of triangles up the Malabar Coast was completed in 1806. Lambton called these triangles the Great Arc series. He later extended the series towards Cape Comorin, and new base lines were measured at Coimbatore in 1806, at Tanjore in 1808, and at Tinnavelly in 1809; the primary triangles were then extended to the sea shore at Pernal, 12 km northeast of Cape Comorin. The arc series was then completed from Cape Comorin to Bangalore.
With this triangulation behind him, Lambton started the northward measurement. A base was measured at Gooty, with triangles connecting it with that near Bangalore and another extending to Thungabhadra. This formed the foundation of a series of triangles across the peninsula, connecting Masulipatnam with Goa.
In 1815, Lambton measured another baseline as part of the Great Arc series: it was in the vicinity of Bidar, at a station called Dumargidala. In 1818, George Everest joined Col. Lambton. In 1822, Lambton continued the survey from Hyderabad towards Nagpur. He died on the road at Hinjunghat on 20 January 1823.
Lambton's contribution is significant. He measured the arc of the meridian near to the equator, and his measurement was used to derive the ellipsoid of the Earth. But his work did not receive the attention it deserved from the scientific community till the fag end of his career. The French recognised his work earlier than the British. In 1817, Lambton became a corresponding member of the French Institute. In 1818, the Royal Society of London made him a member. After this recognition, the Governor-General took the trigonometric survey
under his control and named it The Great Trigonometric Survey of India; Lambton was made the first superintendent of the GTS. He completed the triangulation of 423,276 km in the peninsula.
After Lambton's death, Everest assumed control of the Great Trigonometric Survey. In spite of serious illness, he continued the measurement of the arc, reaching the Tropic of Cancer in May 1824. He completed the astronomical observation at Kalianpura in that November.
Colonel George Everest
Joseph Olliva extended a longitudinal series of triangles from Sironj to Calcutta. It was completed by July 1832, covering a distance of 1120 km.
During the absence of Everest, who went on leave to London for medical treatment, no significant progress was made in the measurement of the Great Arc. When he returned, Andrew Waugh and Patrick Renny joined him to completion the work.
Some 35 stations between Sironj and Dehradun were selected for measurement. A base line was measured in an area around Dehradun in 1834Ð35, and an observatory was established at Kaliana for making astronomical observations.
Innovative methods were used to connect the two base lines. Since most of the area was a flat plain, masonry towers 20-30 metres high were constructed. Everest developed ray tracing methods of locating the stations and introduced the grid iron system of triangulation coverage. Assisted by Waugh, Everest connected the Dehradun base with that of Sironj in February 1837.
Accuracy was an obsession. It was claimed that the difference between the length of the Dehradun base line as measured and as completed by triangulation from the Sironj base line, was only 183 mm.
Everest, Waugh and Walker continued the longitudinal series of the Great Trigonometrical survey and completed it in 1866.
If one looks back at the GTS, 200 years after it was conceptualised and 135 years after it was completed, certain interesting features emerge. The immediate task of the Great Trigonometrical Survey was the accurate determination of the position of important points to form the basis for geographical and other surveys and maps. Lambton also wanted to determine, by actual measurement, the size of the Earth.
However, the other primary objective of the GTS the accurate determination of the position of important points over the country was never achieved. A triangulation may be simple in concept, but its implementation has always been difficult. It is slow and costly. Moreover, the relationship between triangulation extent and cost is non-linear. Too slow and too costly. Almost all topographical and cadastral surveys in India were undertaken before the general triangulation could reach them. As a result, they were anchored to inconsistent reference points and could not be joined to build a systematic map of the whole country. Furthermore, a single coherent survey organisation that would properly implement a systematic survey did not exist. All British survey activities were supposedly unified in 1878 by the formation of the Survey of India, of which the GTS became the Geodetic Branch, but establishing a uniform approach and uniform goals across the country proved impossible.
Not least of the problems was that although the GTS was supported as a great scientific endeavour, the government of India had more pragmatic interests. The administration needed geographic information and small-scale maps for ruling and exploiting the country. For this purpose, in the 1820s the Atlas of India project was established. The aim was to provide a nationwide series of maps at four miles to the inch (1:253,440). This would bring together all the topographic surveys and warp them to fit GTS in order to create a definite cartographic representation of India (Matthew H. Edney, Mapping an Empire, 1999, p 30). The Atlas embodied the British view of India in 1820, fixed, eternal, imperial and known to the British through scientific observation.
This view continued through the 19th century into the 20th century. Even after independence, the preparation of 1:250,000 maps was given undue importance. According to Edney, Map making was integral to British imperialism in India. The surveys and maps together transformed the subcontinent from exotic and largely unknown region into a well-defined and knowable geographical entity. The empire might have defied the maps extent, but mapping defined the empire's nature.
The history of the Great Trigonometrical Survey is relevant to us today as we stand on the cusp of another revolution in map making. GTS was considered the best scientific way of mapping India. Yet in spite of ardent support from the highest echelons of Imperial Britain, it did not satisfy the mapping requirements of India. As a concept it was ideal, but in practice it was riddled with insurmountable problems. Today, GIS and GPS throw up expectations as great as GTS did in the 19th century. Time alone will tell how well these expectations can be fulfilled.
Professor KS Sivasami is in the Centre for Study of Regional Development, School of Social Sciences, Jawaharlal Nehru University, New Delhi 110067; ph: +91-11-618-0244. This is an edited version of an article that first appeared in GIS@Development magazine.
