Many textbooks and journals deal fully with the theory of Aerial Survey in all its aspects. The paper therefore deals with the cost of and the accuracy to be expected from contour surveys made from aerial photographs. This is of some interest to engineers. The cost of both small scale and large scale aerial surveys, based on the experience gained during the last seven or eight years by the Trigonometrical Survey Office as well as by the Department of Transport is given. The errors to be expected in both height and position are examined from the point of view of actual maps made from air photographs and the checks undertaken in the field. In general it was found that in large scale contour surveys (500 feet to the inch or larger) the error in height should not exceed 002 per cent of the height of the aircraft above ground levels. Positional displacements of under a foot were found where the co-ordinates obtained by means of photogrammetric instruments were transformed to the National Grid and then compared with those determined by a land surveyor surveying for title to land.