It is a fact that in the past demographers have concentrated on the global aspect of urbanisation. They have focused on measuring the intensity and pace of urban development, analysing the development of urban networks, and measuring migration from rural to urban areas, in the majority of cases considered as definitive. The analysis of populations at an inner-urban level has delegated to urban planners not necessarily best prepared methodologically for dealing with such issues. However, in the context of decentralisation, a general trend in most countries in recent decades, the need for information for local authorities has constantly increased. As long as clouds are not in the way this enables an almost constant observation of any point on the Globe.
Satellite pictures enable a global analysis of urban areas, including unofficial urban developments.
Following the example of cities in developed countries which started the movement in the 70's, there is an increasing demand among cities in developing countries for Urban Information Systems. For the most part this demand is being met by bilateral or multilateral cooperation agencies. Thus, during the last twenty years, in conjunction with the development of remote sensing there has been a development in the use of Geographical Information Systems in urban areas. Although satellite imagery is the most important source of information in urban information systems the integration of satellite images within these systems fosters a multi-source and combinatory approach. This approach enables a more profitable exploitation of satellite imagery through a more precise distinction of the information useful for the research at hand amid all the data contained in the image and greater efficiency in the methods of extracting information it contains.