The Task of Measuring India



Do you think studying Grade 10 trigonometry didn’t help you in life?

Well think again, because it did much more than give many a persistent feeling of helplessness… it helped measure one of the largest and most interesting land masses in the world, the Indian subcontinent.

A Survey Team, Idaho, 1918
A Survey Team, Idaho, 1918|Wikimedia Commons

When you think of the word survey, your mind conjures up images of hard-hatted municipal employees armed with liquid-filled levellers and never-ending steel tape. They are the constructionwallas in the urban trenches who always seem to be on a quest to find some truth, based on summary readings, while you peer out from the bus window, grateful for your cushy desk job.


John Keay noted in his book, ‘The Great Arc,’ that it was ‘the longest measurement of the Earth’s surface ever to have been attempted.’

But a survey can answer far larger questions about the shape of the world we live in, quite literally in fact as you will find out. That is what happened in the Great Trigonometrical Survey of India, undertaken between 1802 and 1841. The historian John Keay notes in his book ‘The Great Arc,’ that it was ‘the longest measurement of the Earth’s surface ever to have been attempted.’

John Keay book ‘The Great Arc’
John Keay book ‘The Great Arc’|Amazon India

The year was 1802. The British had just wrested control of Mysore from Tipu Sultan. It was also the year an officer under the famed General Wellesley embarked upon a scientific survey to map and measure all the land in the Indian subcontinent that the British now owned, but had little knowledge of.

Aiming to map the territory from Madras to Mangalore, starting from St. Thomas Mount in present-day Chennai, the survey would take on Odyssey–like proportions by the time it was completed in 1841, almost four decades later.

Lt. Col. William Lambton, 1822
Lt. Col. William Lambton, 1822|Wikmedia Commons

The man behind the effort was Lt. Col. William Lambton, an unassuming genius with a great love of the land he set out to survey.

The survey began with a simple measurement of the distance between a flagpole on Madras Beach and the grandstand at the Madras Racecourse. This was to be the baseline; the starting reference point. It was measured with a 100ft-long chain and was 5.85 km long.

Madras (Marina) Beach, Madras, 1913
Madras (Marina) Beach, Madras, 1913|Wikimedia Commons

Having calculated the baseline, Lambton now had the relative position, distance and height of the hill to the beach and grandstand. Lambton then picked another hill a few miles and measured its horizontal angle and elevation, relative to the first hill and the grandstand.

This would give him the second hill’s position, distance and height from the first hill and the beach, and help mark its coordinates on a map. The process was called triangulation, as these distances were calculated using trigonometric formulae.

The first triangulations by Lambton across the Indian peninsula, 1811
The first triangulations by Lambton across the Indian peninsula, 1811|Wikimedia Commons

Lambton would follow this method, walking hill-to-hill with his team, pinning the location of each hill he encountered on the way. When he found the plains of the Cauvery delta too difficult to map, he used the temple tops or gopurams, such as that of a famed Tanjore temple, for his measurements.


When he found the terrain too difficult, Lambton used temple tops or gopurams, for his measurements.

On one occasion, he accidentally dropped one of his heavy instruments off the sides of the temple, damaging one of the statues. He had to spend months repairing the instrument himself, before starting work again.

As for the replacement for the damaged portions of the temple, legend has it, Lambton had his own face sculpted into the structure. So if you find a distinctly-Caucasian-looking stucco on the eastern side of the Brihadeeswarar temple next time you visit, you have a theory to back it up.

Brihadeeswarar Temple, Thanjavur
Brihadeeswarar Temple, Thanjavur|Aravindreddy.d via Wikimedia Commons

In three years, Lambton successfully mapped the 660km east-west distance from Madras to Mangalore in this fashion.

The man was not done though, having tasted success, he set out to map the north-south expanse of British-controlled India, starting from its southernmost point in Kanyakumari.


The Survey helped answer a fundamental scientific question-was the Earth a perfect sphere?

His ambitions were not restricted to mapping of British territory though. His ultimate quest was really to determine the shape of the earth. India would therefore play a central role in the answering of a fundamental scientific question-was the Earth a perfect sphere?

Earth as seen from Apollo 17
Earth as seen from Apollo 17|Nasa via Wikimedia Commons

Lambton named the project the Great Indian Arc of the Meridian, a meridian being an arc of longitude running north-south on the Earth’s surface, of which the Arc was a large section. Lambton’s team was called the Great Trigonometrical Survey of India.

The survey was done manually, and it was slow and cumbersome. This was the pre-computer age after all!


The Survey was done manually in its entirety, with instruments weighing 50 kg

The instruments of choice were a theodolite that weighed 50 kg and a zenith sector. The theodolite was an instrument to measure vertical and horizontal angles on land for triangulation and contained finely calibrated micrometers, microscopes and spirit levels to provide precise measurements.

To ascertain the positions of the stars relative to the land position and thereby calculate the length of a degree of latitude in miles, Lambton used the zenith sector, which was essentially a telescope attached to a 5ft-long sector or tube that pointed straight up to the skies.

Lambton’s Theodolite
Lambton’s Theodolite|Royal Geographical Society

With 150 escorts, signalmen, porters, mahouts and runners, Lambton’s team grew steadily. Lugging the theodolite and other instruments, pitching tents, cooking food and planting flags atop newly-surveyed hills formed the majority of their duties. They also had to hack through impenetrable jungles and undergrowth on their journey, sometimes taking weeks to traverse a few miles.


Lambton’s team had traversed 700 miles of India (around 1,020 km), or 10 degrees of latitude of the Earth’s surface, by foot

Wild rivers, wilder animals and insects, heavy rain and diseases like the “Malabar ague” and “Yellapuram fever” were significant obstacles. Team members were routinely afflicted by fevers, injuries and in some cases, death.

They chased this dream over 13 years. By 1818, Lambton and his men had traversed from Kanyakumari to Hyderabad-they walked, they measured, they recorded and calculated. They had traversed 700 miles of India (around 1,020 km), or 10 degrees of latitude of the Earth’s surface, by foot. Surveys in England and France paled in comparison.

George Everest, 1866
George Everest, 1866|Wikipedia

Lambton had mapped the south of India with inch-perfect accuracy and an error rate of a mere 0.002%. He had discovered that Earth was not spherical, but cut a unique grapefruit-like figure. He had revised the compression of the Earth’s spheroid shape, a calculation first put forth by Sir Isaac Newton himself.


The Great Trigonometrical Survey of India had an error rate of 0.002%

As word of Lambton’s work spread, he received further support to take the project northwards— and thus complete the Great Indian Arc from south to north. It was then one evening in 1818, in his Hyderabad office, that he met his newly-appointed assistant—George Everest.

Illustration of George Everest’s assistants setting up a reference point 
Illustration of George Everest’s assistants setting up a reference point |The British Library

With help from Everest and his ever-growing team, Lambton trekked up the length of India towards Nagpur, eventually hoping to reach Agra. But fate had other plans for him.

Hardly ever ill on his long journey, in 1822, Lambton was in Hinganghat near Nagpur, and had just recovered from a bout of tubercular cough. He had a drink of madeira to celebrate his good health and went to sleep.

He never woke up.

Measuring the Calcutta Baseline, 1832
Measuring the Calcutta Baseline, 1832|Wikimedia Commons

Lambton had abruptly left his dream project behind, with big shoes to fill. His mountain of responsibility thus fell on Everest's shoulders.

Everest wanted to improve upon Lambton's work by basing the survey on a rigid framework. From Kalianpur in Madhya Pradesh, approximately the centre of India, Everest conceived of covering the length and breadth of the country.


Everest completed the Arc up to Banog in the Himalayas near Mussoorie, a length of 2400 km.

He redesigned the theodolite and made it more compact, replacing the steel chain with more portable 10-foot bars. Everest completed the Arc up to Banog in the Himalayas near Mussoorie, a length of 2400 km.

Later, in 1830, he was appointed the Surveyor General of India, but instead of focusing on the Empire’s infrastructural needs, Everest continued to devote himself to the Great Arc.

Great Trigonometrical Survey Tower, Kolkata, erected in 1831, led by George Everest
Great Trigonometrical Survey Tower, Kolkata, erected in 1831, led by George Everest|Biswarup Ganguly via Wikimedia Commons

The Great Arc of the Meridian was finally completed by him in 1841. It spanned 1600 miles along the spine of India and still is the largest meridian arc to be calculated anywhere in the world.


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