Development of Air Survey in North America & Canada: Views of McKinley and History of Development (Especially for GATE-Geospatial 2022)

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McKinley, speaking principally of conditions in the United States in 1929 says:

“In the single decade since the World War, aerial photography has progressed from crude rule-of-thumb work to that of science. Cameras and instruments are improved to a degree which at last makes accurate work possible … Engineers are gradually accepting aerial photography as a sound supplementary mapping method. It seems inevitable that the aerial survey must, in time, become indispensable for mapping. In mapping inaccessible territory, the aerial survey has already assumed priority as shown by the success of the Hamilton-Rice Expedition in mapping hitherto inaccessible regions in tropical South America … Considering the map as a representation of detail on the Earth՚s surface, the aerial camera records these details in a manner impossible to obtain by any other method … Air survey has justified its existence as a surveying method by its two outstanding factors, namely speed, and recording of detail.”

Surveying from aerial photographs was taken up seriously in the United States after the War. The United States Geological Survey is responsible for the mapping of large areas at medium scales. In 1920, using the tri-lens camera the systematic air survey of Santa Domingo and Haiti was commenced. In 1920 a quadrilateral about fifteen miles square was mapped from single-lens photographs, contours being fixed by ground topographers. It was estimated that there was a saving of $ 6.77 per square mile. In 1921 the Topographical Branch of the United States Geological Survey formed a Section of Photographic Mapping.

It must be remembered that the problem was quite different from that in Great Britain because large areas were not adequately mapped topographically. In 1924 after careful investigation stereo-photography was taken up and stereoscopic plotting machinery installed. Although the procedure was quite satisfactory for planimetry, the use of air photographs for contour mapping did not become assured until 1933 when the first Zeiss Multiplex Aero projector was installed.

The area covered by air photography in the United States up to June 1938 is shown in below Figure. This diagram is self-explanatory. The greater part of this photography has been done for the various agencies of the United States Government, including the Geological Survey; the Coast and Geodetic Survey; the Tennessee Valley Authority; the Corps of Engineers, U. S. A. ; the Brazos River Conservation Authority; and the Soil Conservation Service, the Forest Service, and Agricultural Adjustment Administration of the Department of Agriculture.

The area given in the diagram is the total area covered and does not include re-photography of some areas where photographs are no longer suitable. Thus the Department of Agriculture in the U. S. A. photographed or arranged for the photography of 1,582, 052 square miles between 1926 and June 1938.

In Canada, while vertical photography has been used extensively, oblique photography was, and is, used widely in the Laurentian Shield country where there are little relief and much coastline. In this small-scale work, flying control is not so vital and the camera was hand-held at first but now more rigid mountings are used, ensuring that the horizon shows in the photograph. The Canadian air photographic library has increased from 22 photographs in 1922 to 780,000 in 1938.

United States

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