Bengaluru and the story of Great Trigonometrical Survey undertaken across the country

Indian Express

06-05-2025

Maps are something we now take for granted. While driving from one corner of Bengaluru to another, the accuracy of applications such as Google Maps or other GPS devices is not something the average traveller questions. But centuries ago, in the early years of the British Raj, the making of accurate maps was the business of empires–in the case of India, it was an immense endeavour that would take a lifetime to complete.
It also pays to consider the background against which the Great Trigonometrical Survey of India was undertaken. Even in death, the spectre of Tipu Sultan would have loomed over the British. Barely 20 years earlier, Hyder Ali and Tipu had trapped and destroyed a British force at Pollilur, with over 2,000 fatalities. A thorough mapping of the country they aimed to rule would therefore be imperative.
To simplify a rather complex process, the Great Trigonometrical Survey involved measuring a series of immense triangles across the country to enable the proper mapping of the land and the verification of latitudes and longitudes of specific places. In these calculations, the baseline of the triangle would be crucial in maintaining the accuracy of the overall measurements. As recorded by British civil servant F C Danvers, the original intent was to 'throw a series of triangles across from Madras to the opposite coast, for the purpose of determining the breadth of the peninsula in that latitude, and of fixing the latitudes and longitudes of a great many important places'.
The mind behind this project was then Captain ( and later Lt Col) William Lambton, who had previous survey experience in America and had joined the 33rd Regiment in 1797. While he formally began what would become the Great Survey in 1802 in Madras, it seems that a trial run of sorts was carried out by measuring a baseline near Bengaluru in 1800.
The measurement for this baseline was a chain of blistered steel measuring 100 ft exactly at 62 degrees Fahrenheit. The chain had an interesting history–it was originally rejected as a gift by the emperor of China. Some of the survey instruments that were used are on display at the Science Gallery in Hebbal.
The official survey in the Bengaluru area was done in 1804. The Great Trigonometrical Survey across the country would take seventy years to complete–outliving Lambton. The precision measurements made by the survey proved well worth the effort and unearthed several problems with the old measurements. As Danvers put it, 'The distance from Madras to the opposite coast, in the same parallel, was ascertained to be very nearly 360 miles; whereas, until then, the best maps made it exceed 400 miles. All the principal places on the old maps, which had been fixed astronomically, were also found considerably out of position: for example, Arcot was out 10 miles.'
Engineer P L Udaya Kumar, who heads the Mythic Society's 3D digitisation efforts for ancient inscriptions, has also researched the history of the Great Trigonometrical Survey in Bengaluru. Speaking to indianexpress.com, he said, 'The original line was between Krishnarajapuram and Agara…wherever he measured in Bengaluru, he left marks. There are such marks from Kolar, Magadi, Hosur and other places.' He explained, 'Sometimes there would be a cross marked on stones. If there was no boulder, they would place a mound there.'
Udaya Kumar noted that as far as Bengaluru is concerned, the original structures from Lambton's time have not survived. 'Those points were measured multiple times and if the marker was crumbling, they would have been rebuilt,' he said.
Within Bengaluru itself, two of the structures that remained in Bengaluru were a structure on the Hennur-Bagalur road in Kannuru and a tower in Sampigehalli. Regrettably, the former, dating back to 1865, was largely demolished in June last year overnight. The revenue authorities had also filed a case against unknown people in the matter.
Lalbagh also has an interesting, if indirect, connection to the project. At some point in the 1800s, it had come into the private possession of one Gilbert Waugh for several years. His son Andrew would go on to head the Great Trigonometrical Survey project after Sir George Everest and may have indeed named the mountain after him.