Mapping from space for developing countries

Mapping today is a data acquisition for Geo Information Systems (GIS). Maps are just one form of the output of the geoinformation. Geoinformation are important as basic information for any planning purpose, nevertheless the term mapping is used for such data acquisition. Without such information no modern administration of a country is possible. In several developing countries no actual geoinformation and no regular update exists. Classical, the data acquisition is based on aerial images, but not in all countries photo flight equipment is available and foreign photo flight companies can enter some countries only with extreme bureaucratic effort, causing a delay of photo flights and raising the price. The problem of control point determination for mapping purposes today is solved by GPS-positioning, which can be improved by world wide satellite reference systems like Omnistar to absolute accuracy up to 30cm. With the high and very high resolution optical satellites a competition to aerial images exist. The highest resolution system operational now is QuickBird with 61cm ground sampling distance (GSD) corresponding to a photo scale of approximately 1 : 20 000. This will be improved by the successfully launched WorldView-1, always delivering the first images which will be distributed with 50cm GSD, but the operational use for civilian purposes will not start before spring 2008.
For topographic maps not in every case the highest resolution is required. Based on long time experience satellite images with 5m GSD can be used for mapping in the scale 1:50 000 or approximately 0.1mm GSD is required in the map scale. For three-dimensional point determination stereo pairs are required. From the very high resolution satellites only few stereo pairs, taken from the same orbit, are available, but this is partially solved by the stereo systems Cartosat-1 and ALOS-PRISM. The image quality of ALOS-PRISM is still not optimal, but the images can be used for the generation of digital elevation models (DEM). The geoinformation also can be generated by on-screen digitizing if a DEM exists. Beside the possibility of the generation of height models by automatic image matching, DEMs can be bought also based on the stereo system SPOT-5 HRS, but for several purposes the nearly world wide available SRTM height model can be used.
An overview about available imaging systems, the possibility of DEM generation as well as detailed description about the possibilities and limitations of the SRTM height models will be given as well as on overview about the experimental relation between GSD and possible map scale. The geometric and information potential of the serious of high and very high optical satellite images will be demonstrated.