In an age when vast swathes of the world remained unmapped and mysterious, maps were more than navigational tools—they were instruments of power, knowledge, and ambition. In the late 18th century, as European empires scrambled to define and dominate distant lands, accurate cartography became a prized asset. It was against this backdrop that James Rennel undertook the first large-scale survey of India in 1782, producing the Map of Hindoostan through rudimentary route surveys. Rennel’s efforts were merely the prologue to a far more audacious endeavour: the Great Trigonometrical Survey (GTS) of India, an epic scientific undertaking that spanned nearly a century. In their new book India in Triangles, authors Shruthi Rao and Meera Iyer chronicle this extraordinary project.
Commissioned by the East India Company in 1802, the GTS was born out of imperial necessity. As the Company extended its dominion, the need to measure, classify, and control the land became ever more urgent. The GTS sought to map the entirety of the subcontinent—including the vast and forbidding Himalayas—using cutting-edge trigonometric methods that, for their time, represented the pinnacle of surveying science. “We split the story into easily understandable chunks, provided a lot of context at every turn, so that it could be easily understood,” says Rao. “We tried to ensure the main narrative flows like a story and provided boxes or sidebars for those who would like to learn more.”
The GTS relied on triangulation—measuring angles between distant points to calculate position with remarkable accuracy—and demanded an almost monastic discipline in method. The authors ensure these sophisticated concepts remain accessible. What India in Triangles does so deftly is connect this arcane imperial project to the present day. “I hope the book makes children and adults go out and look for remnants of the GTS scattered all over India,” says Iyer. “Imagine if we could curate a citizen-created database of all the GTS relics—benchmarks, towers, baselines, etc.—that would be cool!”
The book closes with a set of thoughtfully designed activities, inviting readers—particularly students and math enthusiasts—to explore the underlying trigonometric principles hands-on. It is a fitting conclusion to a story that is both historical and mathematical, scientific and human. With its lucid prose, scholarly depth, and narrative elegance, India in Triangles is more than a chronicle of surveying—it is a meditation on the ways in which land, knowledge, and empire intersect, and a tribute to those who quite literally shaped the map of India.