Topographic mapping from satellite imagery in Africa

Abstract

The paper first reviews the situation regarding topographic mapping in Africa. While for some countries, the main concern is the production of new base maps, for many other African countries the main problem is the revision of a large number of existing maps which are now thoroughly out-of-date. The situation prevailing in most African national mapping agencies is then outlined and the availability of satellite photography and scanner imagery over Africa is then discussed. The results of tests of the accuracy and the content of topographic maps derived from satellite imagery conducted over a number of test sites having different landscape characteristics are summarized and discussed. Next some examples of topographic mapping from stereo-SPOT imagery are described, including those from Ethiopia, Djibouti aid Guinea. This is followed by further examples of purely planimetric line mapping from Nigeria and image mapping from Central Sudan, using monoscopic SPOT and TM images respectively. This leads on to a further discussion of a UNDP-supported national map revision programme carried out over Uganda. The paper then goes on to make a comparison of the respective attributes of small-scale aerial photography and satellite imagery for topographic mapping in Africa and concludes with a short discussion of the likely impact of the availability of higher resolution satellite imagery which is promised for the near future.