The "Canadian" method--if I may call it so; for although it was invented and has been used elsewhere, it has been far more extensively applied in Canada than in any other part of the world--may be briefly described as "plane-tabling by photography." It requires, equally with the plane-table, an accurate framework, on which to base the detailed survey; and simply substitutes a small (3-inch vernier) theodolite and camera for the sight-rule and plane-table. Stations are fixed and photographs oriented by means of the theodolite; the photographs, which are taken so as to be as nearly as possible true perspectives, represent the country as it would be seen by the plane-tabler, and detail on them may be fixed by intersections or sketched in by eye in exactly the same way as on the plane-table. Angles are read and photographs taken in the field; and, if considered necessary to test exposures or protect photographic plates from deterioration due to climatic conditions, development of plates is also carried out there. Otherwise, the map is made wholly in the office, using either contact prints or enlargements, from the negatives taken in the field. The latter are usually preferable. The main advantages at high altitudes over the plane-table are, that a much larger area can be covered in a given time in the field, that the instruments are more portable for difficult climbing, that there is no necessity to do accurate drawing with numbed fingers, and that the draughtsman may see the country from several points of view at one time. On the other hand, more equipment is necessary, and--a great disadvantage sometimes, as in this case--the map does not come into being as one goes along. After carrying out various preliminary adjustments and tests at the office of the Trigonometrical Survey at Dehra Dun, I reached Darjeeling on April 30, and Tingri on June 19, travelling with Expedition Headquarters via Ph[=a]ri Dzong. _En route_ Tingri, we had caught glimpses of Everest and the neighbouring peaks; so that by the time we arrived there, I was able, with the help of the existing maps and what local information we had obtained, to decide on the area I would attempt to survey. I say "attempt," for little was really known then about the geography, and still less about the weather conditions throughout the summer. As it turned out in the end, the area had to be much curtailed, and certain parts surveyed in considerably less detail than I should have liked: almost wholly on account of the weather. Although it was often fairly clear at 6 a.m. or so, photographs taken before 8, particularly at the latter end of the season, were of little use for surveying purposes.