The Great Trigonometrical Survey of India started on 10 April 1802 with the measurement of a baseline near Madras. Major Lambton selected the flat plains with St. Thomas Mount at the north end and Perumbauk hill at the southern end. The baseline was long. Lieutenant Kater was despatched to find high vantage points on the hills of the west so that the coastal points of Tellicherry and Cannanore could be connected. The high hills chosen were Mount Delly and Tadiandamol. The distance from coast to coast was and this survey line was completed in 1806. The East India Company thought that this project would take about five years, but it took nearly 70 years, well past the Indian Rebellion of 1857 and the end of company rule in India. Because of the extent of the land to be surveyed, the surveyors did not triangulate the whole of India but instead created what they called a "gridiron" of triangulation chains running from north-south and east-west. At times the survey party numbered 700 people.