The first rigorous survey undertaken in the neighbourhood was that carried out by Captain C. H. D. Ryder, R.E. (now Colonel Ryder, C.I.E., D.S.O., Surveyor-General of India), during the Tibet Mission of 1903-1904. During the stay of the Mission at Kampa, the 1/4-inch survey was carried as far West as longitude 88 deg.; while, on the subsequent return march up the Tsangpo Valley, surveys were extended as far as the Southern watershed of the great river--the so-called Ladak Range--in latitude 29 deg. approximately. West of longitude 88 deg. there thus remained a stretch of unsurveyed country some 14,000 square miles in area, between the Ladak Range on the North and the Great Himalaya Range on the South--the latter forming the Northern frontier of Nepal. The Mount Everest Expedition provided an opportunity of making good the whole of this area, with the exception of some 2,000 square miles at the extreme Western end, into which, in view of the restrictions of the Indian Foreign Department, I did not feel justified in penetrating. Fortunately, Colonel Bury's plans contemplated an outward Northerly journey via Shekar and Tingri to the Western flanks of Mount Everest, whence the reconnaissance of the mountain was to be carried out from West to East, parallel to the Northern frontier of Nepal. This rendered feasible the mapping of the whole unsurveyed area between the Southern watershed of the Tsangpo and the Great Himalaya Range, as far West as longitude 85 deg. 30', without in any way infringing the Foreign Department's orders and restrictions. For the purpose of the detailed survey of the Mount Everest regions, it was arranged for my Assistant, Major Wheeler, to make a thorough test of the Canadian pattern of photo-survey apparatus, of which he had had previous experience in the Canadian Rocky Mountains. This method of survey, which had not hitherto been employed in India, is particularly adapted for use in high mountain regions. Fortunately, the experimental outfit, which had recently been ordered from England, was delivered just in time to accompany the Expedition. Wheeler's account of his season's work will be found in Appendix II. With a view to carrying out the revision survey of Sikkim while awaiting the arrival of the members of the Expedition from England, the Survey Detachment was authorised to assemble at Darjeeling early in April, six weeks before the date fixed for the start of the Expedition. In spite of an unusually wet and cloudy spring, the three surveyors made such good use of their time that 2,500 square miles of country were completed before the advance of the Expedition necessitated the temporary abandonment of this work.