The Great Trigonometric Survey of India reached Himalaya early in the 19th century and because it was in the British Raj the Garhwal District (once the Garhwal Kingdom and after independence a division now in the state of Uttarakhand) was surveyed before the Nepalese and Tibetan regions. By 1820 the highest mountain to have been measured was Peak XIV in Garhwal Himalaya at . It had the local name of Nanda Devi and it remained the highest known until 1847 when Kangchenjunga was measured. Some geographers doubted a height as great as this and thought it had been overestimated - it is now known the overestimate was only . The survey also identified a ring of very high mountains encircling Nanda Devi and it identified this region, and not Lake Manasarovar, as the source of the river Ganges, or Ganga.