The large increase in world population, desire for better standard of living, and the desire for a better quality of living have placed great demands on the Earth’s resources renewable. The available resources must be surveyed and quantified; their consumption must be periodically monitored. Monitoring implies repeated surveys. The effect of human activity on the natural environment also needs to be closely monitored in order to prevent the degradation of the environment and to plan its improvement. It is also necessary to identify the sources of degradation and take prompt corrective measures.
Ground surveys over large areas are too slow, too subjective and in the long run too expensive to fulfil the functions described above. Aerial photogrammetry and remote sensing techniques have now become the main tools for this purpose.
Aerial photography started more than sixty years ago as a reconnaissance tool; it then acquired a photogrammetric quality and enabled topographic maps to be produced; in recent times it has been used to generate thematic maps. Aerial photogrammetry mapping still depends mostly in visual analysis and interpretation techniques. Modern aircraft and satellite remote sensing techniques acquire data in digital form over many bands of the electromagnetic spectrum. The data is analysed and interpreted on computers by photogrammetric softwares; even the maps are drawn through an automatic cartographic instrument driven by computers or capturing it manually. All the above techniques can fulfil the demands of a fast, versatile survey and monitoring system. US, India and other developed countries has made rapid strides in this direction.