Scenarios of city's evolution between urbanization and deurbanization

The processes of urbanization affecting the modern world have seen the explosion of the city and the transformation of compact and well defined structures in agglomerations with a seamlessly expansion. This has sparked a number of social and economic consequences that have impacted on the city, on the urbanized area, and on the surroundings. The usage of the term "sprawl" to define the process of expansion of the human agglomerations dates back to 1937, as Nachiba and Walsh (2004), and from that year countless researches, papers and books were done on the argument. But it is open the question about the future trends of the city and the possible evolution of this human product. If it is clear that the expansive model is still winning (and may be expected to keep it, given the intrinsic conditions governing today's economic processes), it is equally necessary to identify new models that can better interpret the needs for a new attention to the territory and its environment. For this purpose the paper explores the feasible use of the scenario analysis - also if at a preliminary phase - as tool for defining the possible evolutionary paths of the city. Particular attention is placed on the construction of de-urbanization's scenarios, namely the set of reorganization's hypotheses of urban structures focused on the compaction of their physical size and on the maximizing of the number of residents and users. Historically the de-urbanization processes are not a novelty. At the peak of its power Rome, centre of one of the largest ancient empires, had over a million of inhabitants, while at the time of national unification (1870) it had fewer than 100,000, spread over a much smaller urban area bounded by the Aurelian Walls (Mazzeo 2011); such cases occurred frequently throughout history, even with more radical processes that led to the physical disappearance - and often of the same remembrance - of the cities. The paper seeks to deepen the possible trajectories of de-urbanization and of urban and territorial reorganization stretched to reverse the diffusion and expansive processes at the metropolitan level. For this purpose the paper initially defines the characters of the processes of urbanization, also with reference to some research's models. The second part investigates the use of scenarios for the construction of evolutionary trends. The third, finally, examines the trends comparing the processes of urban growth and of de-urbanization.