Both in its classical and contemporary versions, social ecology (which remains, despite all possible criticisms of the originator, the most substantial body of empirical knowledge on human settlements) is based on a version of the analysis of competition of different human groups for living space. It is true that in social ecological analyses many other functions are equally considered, but the residential one is largely prominent. Simple evidence of this lies in the fact that the great majority of statistics about cities are based on residential patterns and residential units of observation. On the other hand, it seems quite evident that the new form of urban morphology is largely the product of the progressive differentiation of several populations gravitating around metropolitan centres. With increased mobility of the population in numbers, direction, span and frequency, the relations between population and territory become highly dynamic, and the set of social ecological concepts aimed at reconstructing structures of spatial arrangement are strained to a critical point.
There is little doubt that one of the major issues confronting our society, and the European continent in particular, is the profound readjustment of established equilibria between populations and territory. These can be examined at three levels of analysis.
At the highest level, we have the disappearance of large geopolitical units, such as the former USSR or Yugoslavia, and their substitution with a host of new and often undefined political units, sometimes as new states and sometimes as quasi-states. European integration, albeit in less dramatic ways, has set in motion processes of the same type, as witnessed by the post-Maastricht controversies, and by the generalized growth of regional political movements.
At a lower level, we have the growth and competition of large urban entities competing with each other across national borders, and increasingly playing independent roles in the globalization processes.
At the microsociological level we find the complex interplay of ethnic, class and age traits defining populations with the social ecology of the city. It is a particularly difficult situation when administrative areas in the city interact with culturally sensitive population-identifying morphologies, and social actors try to position themselves strategically inside the invisible network of administrative cages. This process is well-known, under the heading of "redistricting", and it is likely to become increasingly stronger even on the European continent.
Admittedly, the relation between population and land has never been totally stable, as is witnessed by large scale movements such as the shift of the agricultural frontier, the waves of historical migrations and the more recent urbanization dynamics that have given rise to the world in which we live. To be sure, not even the land has remained stable over time, as creation, destruction and transformation of the inhabitable land goes on perennially. Today, however, a new dramatic dimension has been added to this relation through the speed in which, physically or experientially, different points in the matrix of places can be connected with different points in the matrix of persons, social units, and events. This new dimension undoubtedly has far-reaching social consequences that we have recently begun to explore systematically and on which our knowledge is still greatly limited.
Class-based analyses meet equally serious difficulties in a period in which, on the one hand, actors such as social movements, become increasingly visible on the urban scene and, on the other, changes in the structure of the economy deeply affect established class patterns in all the advanced economies as well as in other countries. To give an example of both the simplicity of definition and empirical power of the concept of population, it is sufficient to look at current patterns of urban migration from developing countries to the developed ones. Migration flows are mostly composed of individuals moving according to random personal motivations. The effects of these aggregate decisions are far-reaching precisely because they are a loose sum of individual actions.
When we observe the dynamics that Durkheim, talking about the movement from the country to the city, called "un courant d'opinion, une poussée collective" one can be fairly sure that such currents reflect or anticipate the reactions of the "social inclusion component", to some great mutation of a deep structural nature. A phenomenon of this kind is affecting contemporary cities in these very years when, on the one hand, we can observe the interruption and even the inversion of century old urbanization processes and, on the other, there is a growing renewed interest in urban life where new technologies mix with the new urban middle age population, affecting all aspects of their past life (e.g. migration flows from rural to urban areas).
In the traditional town, the inhabitants, or the population living in the city, largely coincided with the population working in the city. City limits encompassed both these populations in one territory or spatial unit for millenia and were, until very recently, encircled by walls and neatly separated from the rest of the land. The additional population of market-goers, visitors, pilgrims or suppliers, while not irrelevant numerically or functionally, did not deeply affect the social and ecological structure of the city.
The early metropolitan development that took place in the United States from the 1920s, and after War World II in Europe, can be seen essentially as a growing differentiation of two populations: the inhabitants and the workers. From the sociological point of view the class structure of the commuting population is quite different, and actually almost symmetrical in the USA and in Europe, and the urban morphology produced by this differentiation is similar. The result is what's called first generation or early metropolis largely based on a functional urban system (FUR) or daily urban system (DUS), or commuting basins, and is embodied in the concept of metropolitan area.
Some of the same factors that contributed to the first generation metropolis, however, contributed to a further differentiation, in particular the diffusion of private cars and, in general, of fast transportation systems. The increased mobility of people, combined with the availability of greater income and leisure, allowed the differentiation of a third population in the diagram, the city users, namely a population composed of persons moving to a city in order to use its private and public services: shopping, movies, museums, etc,.
The size of the population is growing, but it is difficult to assess precisely because all our collective cognitive apparatus is geared to a traditional city that is undergoing a profound mutation and statistics still deal mainly with inhabitants, and to a smaller degree with commuters, but not at all with users. If we want to perceive these new trends systematically we have to look to entirely new sources of information.
For centuries the top ranking cities of European urban systems embodied the specificity of local culture and traditions.In the competition among these several populations, and related urban functions, it seems quite clear that the residential function and the urban inhabitants tend to be on the losing side. But the entire philosophy of local government is based on various degrees of self-government by the city dwellers.
The main topic may be the renewed assertion that urban systems in advanced economies are undergoing a deep change, not dissimilar in scope and consequences from the one that led to the formation of the industrial town and new social inclusionand exclusion forms. Globalization, transnationalization and internationalization are common terms used in the present literature, but further clarification will be needed because they are not totally synonymous. Globalization is more encompassing, while internationalization has more to do with processes involving nations and their relations. In any case, this process, or processes, can be studied from the point of view of their effects on society at large or for their effects on cities, or system of cities. The issue of governance of these new entities then becomes crucial both for the comprehension of current dynamics and for the action to be taken to influence the future social morphology. Globalization trends tend to "homogenise" cities, all around the world.