Processos de expansão urbana e mudanças na paisagem: ensaio metodológico (1950-2000)

Abstract

The second half of the 20th century witnessed the rapid expansion of built-up areas practically all over the world. In Portugal, this phenomenon took place particularly along the coastal strip and around its two main cities, Lisbon and Porto. Economic and demographic growth led to processes of urban expansion, which in turn bolstered the development of extensive urbanized continuums, contributing to the consolidation of the metropolitan areas and transformation of landscapes. Greater knowledge of the recent processes of urbanization is of interest to the geographical sciences, as well as to applied fields such as spatial planning. Since their initial development, Geographical Information Systems (GIS) and automatic mapping tools have opened new horizons in Cartography, with a potential which should be taken advantage also in the study of landscapes and, particularly, of urban growth. From a morphological point of view, a study of urban expansion necessarily has to be based on multitemporal mapping. More than successive static pictures, multitemporal mapping produces a dynamic image of the process, providing support to ensuing explanatory studies. In Portugal, the studies on urban expansion are limited either by the reduced scale employed or by their reduced focus (studies of small areas or single cities). Increasingly in use, techniques based on the classification and/or interpretation of satellite images produce multitemporal cartography at much larger scale and coverage. However, these techniques have limitations, given their recent development: it is not possible to map built-up areas prior to 1980. The limitations in producing multitemporal urban cartography at regional and sub-regional scales could be mitigated by an approach integrating information from old editions of topographic mapping in a GIS, which could thus track the process of urban growth for a certain time frame. In this paper, this approach was employed to prepare a multitemporal cartographic database of built areas, with three moments comprising the second half of the 20th century. These databases also served to produce a set of "morpho-densimetric" indicators related to built-up areas, for the three temporal moments, leading to analyses on the pace and forms of recent urbanization in the area under study (the Porto metropolis). We believe that the approach proposed can open new perspectives for cartographic production, as well as for the study and understanding of recent urbanization processes and its implications on the landscape dynamics.