Keay's account of this Great Trigonometrical Survey is lively and dramatic, with a focus on the two men who led the survey and whose dedication (if not fanaticism) saw it to completion. William Lambton lies in an obscure grave in central India and a mountain named after him in Canada during his early career was subsequently renamed. But his was the original inspiration for the Survey and he trained the staff who were to be its backbone (and who revered him). His successor George Everest had what is now the world's best known mountain named after him, although he never saw it. He was an acerbic and difficult character, known for his abuse of colleagues and subordinates, though he didn't bear grudges and mellowed in his old age. (They were peripheral to the Arc itself, but Keay also devotes considerable space to the Himalayas, both to the early reports of peaks that might exceed the then highest known peaks in the Andes and to the eventual determination of their heights and Everest's status as the world's highest.)
The Great Arc touches in fascinating ways on science and its history and politics. One obvious connection is to the broader development of geodetic theory and attempts to determine the shape of the earth, though mathematically Keay ventures no further than explaining basic triangulation. There are other insights into the workings of science — one telling story recounts how when the half-ton theodolite necessary for the survey was captured by the French in 1803, they forwarded it on with "a complimentary letter"! And the mapping and surveying of India played a crucial role in the establishment and consolidation of British rule over the sub-continent, both as a foundation for building roads and telegraphs and carrying out land surveys and as an ideological and rhetorical instrument of imperialism. Local discontents with the survey contributed to the tensions preceding the 1857 Revolt.
I read The Great Arc in a day. It is an entertaining little book that connects to a range of subjects — exploration, biography, the history of science, and Indian history — and should have broad appeal.