The recent evolution of the Italian urban network, in addition to the changes connected to demographic dynamics, is linked to the transformations and strengthening of the functions performed by the cities. In particular, these are tertiary functions, that is the range of services present in urban centers and designed to satisfy local demand, that is, regional, supra-regional, national or – in a limited but growing number of cases – international demand.
For a long time the theory that better than any other has been able to interpret the distribution of tertiary activities among the different cities of a region was the theory of central localities, from which the very notion of urban network is derived. Developed in the early Thirties by the German geographer W. Christaller, repeatedly subjected to an update of its logical bases and differently adapted to the multiplicity of regional realities (with studies by A. Lösch, EL Ullman, W. Isard, BJL Berry, etc.), this theory demonstrates how the distribution of cities on the territory is not accidental, but there is a certain regularity both in the arrangement and in the hierarchy of urban centers, the latter being regulated by the different importance of the functions they perform. Urban functions, therefore, they are distributed among the different cities according to a hierarchical principle, ie there is a certain correspondence between demographic consistency and the complexity of the supply structure. This means that in the larger centers there are not only a higher number of services but also services of a higher and higher rank, ie progressively less widespread in the area. Of course, in the most important centers, alongside the higher tertiary activities, they are coexisting also the services of the lower ranks. The resulting territorial scheme envisages a set of cities neatly distributed over the geographic space, with logically interspersed functions, configuring the so-called urban network. This logical construction constituted the main theory of reference for the organizational models of geographic space in the countries of Western Europe (including Italy) and North America, up to the end of the 1950s and part of the 1960s.
The emergence of an advanced development process, which transfers the major driving forces from the secondary sector to the tertiary sector, has however progressively eroded its own interpretative skills to the theory of central localities. The crisis of large industry and the connected affirmation of production methods based no longer on economies of scale but on industrial multilocalization and on the segmentation of the technical cycle of the product, the affirmation of high-techindustries, the explosion of services destined for intermediate consumption (business services), the great progress achieved in the transport and communications sector, are all factors that have contributed to altering the methods of construction of the geographical space, introducing new trends in the localization of services. The spread, especially in advanced economies that are usually defined as having a post-industrial economy, of increasing levels of economic well-being has led to a progressive redistribution of services throughout the territory, thus originating a process of progressive urbanization of the countryside. Consequently, the localization of high-ranking services is no longer a prerogative of medium or medium-large cities, but takes place according to methods of widespread distribution throughout the territory.
According to USAERS, the loss of a correlation between the rank of services and urban dimensions and the consequent change in the principle of coexistence with that of functional specialization are just as many symptoms of the progressive disintegration of the logical construction developed by W. Christaller and his successors. In other words, in the most economically advanced regions of the globe, the geographical organization of the territory based on the hierarchical principle is progressively replaced by a “ reticular ” urban structure, therefore no longer built on vertical integration (hierarchical, therefore) but on a horizontal (territorial) integration, precisely called ” network ”.
In Italy the phenomenon is particularly evident in western Padania, but the north-western regions of Tuscany and in part the Marches are also showing the signs of similar territorial restructuring. The processes of demographic deconcentration, which involved cities such as Turin, Milan, Genoa, but also Rome, Florence and Bologna, could therefore be interpreted as the result of two orders of trends: on the one hand, the fall in population growth which is justified both with the drop in the birth rate and with the arrest of internal migratory currents, and with a certain redistribution of the population in a wider context than the more properly urban one; on the other hand, the availability of diversified services, even at local levels,
Apparently contrasting with the principle of functional diffusion on the territory is the phenomenon of repolarization or re-centralization of cities, a phenomenon outlined by Italian scholars between the end of the 1980s and the early 1990s. This is the process according to which in metropolitan areas of particular importance, such as Milan and Rome (but subordinately also Turin, Genoa, Bologna, and so on), business services are concentrated, characterized by high specialization and therefore defined as strategic, which make these two metropolises two nodal points of the European economic space and not only the Italian one.