Rhodesia completely mapped by its own efforts
A joint programme by the Dept. of the Surveyor-General and the Rhodesian Air Force
In 1970 Rhodesia became the first country in Africa to be completely mapped, by its own efforts, at a scale of 1 : 50 000, which is widely accepted as being adequate for general reconnaissance and development planning. Each 1 : 50 000 map covers ¼ degree latitude by ¼ degree longitude, an area of about 275 square miles. They are used extensively in the layout of farms, reconnaissance for roads, railways, power lines, canal routes, VHF relay stations, wall maps for rural councils, Intensive Conservation Areas and tsetse control.
The Department of the Surveyor-General in Rhodesia has undertaken all the country’s mapping at the 1 : 50 000 scale. In all other African countries the governments call on foreign or private contractors for all or part of this work.
The first of the 581 map sheets which blanket the country was compiled in 1937 when aerial photography at a scale of 1:20 000 was carried out, which meant that some 135 photographs were needed to compile a single map sheet.
During the days of Federation, the photo-scale was changed to a more economic 1 : 40 000 and the published map, which until then had been a plain brown line print, was produced in five colours and depicted vegetation.
In 1962 a $30 000 stereocomparator was shipped out from Rome to provide an analytical approach to the problem of aerial triangulation, thereby vastly reducing the amount of expensive ground survey required.
The new technique was successfully developed by the Department and entailed the writing of suitable programmes for an electronic computer which processes the data supplied by the stereocomparator. To do this the computer uses some 12 000 instructions.
This was quite a feat in itself as few countries even today have completely solved all the technical problems involved in the use of the stereocomparator.
At the same time the Department received the first of its present five stereo plotters which plot map detail to a very fine margin of error. With these modem and sophisticated machines it was possible to use the smaller and therefore more economic scale of 1 : 80 000 aerial photography.
The Rhodesian Air Force was supplied with a precision wide-angle survey camera valued at $12 000 in 1965 and, flying their jet aircraft at the required altitude of 45 000 feet above sea level, they pioneered the use of a precision camera for mapping, from a jet aircraft.
Here is an example of aerial photography as processed in 1978 by the Mapping and Research Unit of the Rhodesian Intelligence Corps (RIC) to an original scale of 1 : 5 000. Although this print of Lions Cave is not the clearest it demonstrates the type of source material from which the 50 thou and 250 thou scale maps were compiled.
The 1 : 50 000 scale map extract below shows how the above photo has been used to compile the map. The homestead and the employees’ compound are both depicted on either side of the road running north – south through Lions Cave Farm. Cultivated areas are shown by brown stipple and reference to the detailed survey photo, in conjunction with a close up of the map, shows that contour ploughing is being practised.
The 1 : 250 000 scale map extract of the Centenary area below shows how the above have been used in turn to compile this map.
For more information on the Air Force Photo Reconnaissance Section please see here: https://rhodesianforces.org/rhodesianforces.org/airforcephotosection.html