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orthophoto map — English
A vertical aerial photograph (see “airphoto”) of a part of the Earth’s surface that has been specially processed to become a most useful type of topographical map. They are large scale photographic maps (1:2 500, 1:5 000, 1:10 000 and 1:15 000) to which contour lines, spot heights and annotations have been added (see “contour maps”, “isometric lines” and “interpolation”). In South Africa the official series is on a scale of 1:10 000, but only the major urban complexes have been covered. Orthophoto maps have one major advantage over topographical maps, namely that they are actual photographs with all the information about that part of the surface captured exactly as it would be seen by the eye. One characteristic of these maps is that – owing to the large scale – it would require 15 or 20 or even more sheets to cover an urban complex like Durban, whereas the entire area could be covered by one 1:50 000 topocadastral map sheet. Under certain circumstances it is more advantageous to use a topocadastral map, but under different circumstances the orthophoto maps cannot be surpassed for the specific detail it provides. It might come as a surprise that orthophoto maps are cheaper to produce than conventional topocadastral maps and therefore easier to update. (See “topographical map”, “cadastral map” and “topocadastral map”.)
