Discusión

A point to be faced prior to any further analysis concerns the meaning itself of the expression ‘urban polarities’. What, then, do we mean to allude to by using this term? Mostly, in urban sociology language, as in those of other disciplines concerning the city, polarity is more or less implicitly considered in Christallerian

terms: it is thus a concentration of service activities possessing relative rarity, which is placed in the centre – with respect to a system of accessibility – of a gravitational area where the users of these activities are localised. In some cases, this use of the word is extended to also include functions in the analysis which have productive features, rather than being a service, or which constitute a service, the users of which are economic activities rather than the final consumers.

The meaning we intend to attribute to the concept of ‘urban polarity’ in the pages that follow is the same as the one emerging from this second, wider use;

moreover, this also seems useful considering the ever-growing difficulty of clearly distinguishing activities producing goods and those delivering services within the framework of postfordist socio-economical systems. Apart from this clarification, however, the idea of polarity is presented here in even wider terms, especially as far as the relationship existing between the concentration of functions and the whole of metropolitan space is concerned, which here will not be understood solely as a division into gravitational basins relating to those functions.

The basic idea is, in effect, that the polarities recognisable in a metropolitan area should correspond not only to concentrations of activities but, simultaneously, also to fundamental nodes of the city’s social and economic relations system, as well as to particular configurations of built-up space and technological configurations fit to support the execution of specific functions. The relations these polarities estab-lish with the territory are undoubtedly defined by their capacity to supply services to users (who, moreover, access them through numerous means of transport and different telecommunication systems); at the same time, though, we also need to take into account the modality by which each pole links up with others, so as to form networks at various levels, as well as its potential for representing (or not) a propulsive factor for a course of local development from which an entire part of the urban territory and the large number of subjects who work in this context may gain benefit, regardless of the fact whether they are direct users of the facilities concentrated in the pole itself.

To develop the ideas rapidly dealt with above an analytical scheme fit to throw light on the different forms of relations between polarities and metropolitan space may be useful. In particular, reference will be made here to a recent contribution by David Harvey (2006), who – on the other hand – takes up again and develops an idea already stated in Social Justice and the City (Harvey 1973): the distinction between three different ways of understanding and representing space.

– In the first way, space is conceived as absolute space. It corresponds to an image of space as a fixed entity, within the frame of which elements can be picked out or events planned. It is interpreted as a ‘thing in itself’; it is the Newtonian space that enables measurements to be recorded and distances to be calculated based on Euclidean geometry. In social terms, it is defined by property rights and limits which create distinct territorial objects within borders (e.g. municipalities, regions, states).

– The second is, vice-versa, a relative space, which concerns representations typi-cal of non-Euclidean geometry and Einstein’s theories. It closely combines time and space dimensions and, moreover, brings into play the point of view of

the observer: thus ‘the spatial frame depends crucially upon what it is that is being relativised and by whom’ (Harvey 2006, p. 122). It is basically a space of flows (money, people, energy, data, etc.); distance in this space – and the friction it causes on the flows – is related to the points of view from which these are considered (e.g. in terms of time, costs, energy consumption, etc.).

– The third is relational space. This is meant by Harvey not as something within which processes take place, but rather as an evolving situation, defined by the processes themselves as they are carried out. And, along this course, each point in the space cannot be understood solely for its specific characteristics, but also as incorporating within it what is around it: ‘A wide variety of disparate influences swirling over space in the past, present and future concentrate and congeal at a certain point. . . to define the nature of that point’ (Harvey 2006, p. 124). So in this way each point in relative space is marked also by the social relations founded on it and the symbolic stratification incorporated in the built-up envi-ronment.

It should be pointed out that these three dimensions of space, though able to give rise to interpretative conflicts, do not impose a final choice between alternative possibil-ities of representation; actually they often need to be kept in mind simultaneously, though maintaining a reciprocal dialectic tension; it is, however, possible that in the given circumstances only one of the three dimensions be taken as decisive for understanding the phenomena examined.

Let us try, then, to use the distinction just introduced to focus on the different features of urban polarities.

The idea of an absolute space serves to highlight above all the aspects which appear in the more traditional definitions of polarities: that is, the physical con-centration of functions in a limited space (at worst representable as a point on the metropolitan territory) and the presence of a gravitational basin, understood as a sphere of user localisation, bearing in mind a given accessibility structure. It is this concentration that defines polarities as specific areas of the city, localised in certain ambits (e.g. in the historic centre, or in a barycentric position with respect to periph-eral quarters); the basin takes shape as a contiguous space that has a given polarity in its centre and the borders of which are represented by lines of equivalence of different polarities’ capacity of attraction. Gravitational basins are of different sizes in proportion to the rarity of the functions present in the polarity; in any case they are of relatively limited dimensions (though variable depending on variations in the transport means considered) in that a material transfer of users towards the polar place is taken for granted.

Vice-versa, consideration of relative space enables the role of polarity to be re-alised in a space of flows, which are not necessarily the movement of social subjects between their homes and the place where they use the services; for the flows to consider are of a different kind, e.g. supplying goods, finance, energy, data, etc. The channels along which these flows run are also of different kinds; in any case, here the role of distance means of communication is much more important than when considering absolute space. The image of the city or metropolitan area deriving

from it is also different: in the case of absolute space this is basically a hierarchical structure made up of areas nested one within the other, whereas here each polarity (and, possibly, each function) is in a direct relationship with a varied space of flows and almost free from ‘natural’ limits (Amin and Thrift 2002). To some extent, then, each polarity has its own positional value; the city and relative user basins are only one of the variables of the flow it confronts. Being plural, the criterion by which the relationship between each polarity and the space of flows should be evaluated, and the importance or hierarchical role of each concentration, can only be measured by referring to specific points of view; there will therefore no longer be absolute metropolitan centrality, but many centralities, that are so in relation to a given reference point, such as capacity to intercept population flows, maximisation of logistic efficiency, possibility to promote property income, visibility and interna-tional prestige and so on.

If the dimension of relational space is then introduced into the analysis, the rep-resentation that ensues is again different. For in this light polarity is not so simply because of the concentration of the functions it accommodates, nor just for its ca-pacity to link up with a network of flows; it draws its value also from the context in which it has settled and the potential relations it establishes with it.

We might rather say that it takes on a role in that it has relations with its envi-ronment, provided we give this term a wide meaning and do not refer solely to the physical/biological dimension of the term.² A polarity, then, is such in relation to a complex of environmental resources – in a stratified form – accumulated on the territory through a wide variety of processes, from those of natural evolution to the spatial effects of subsequent processes of territorialisation and deterritorialisation (Raffestin 1984, Turco 1988), reaching forms of accumulation of immaterial fac-tors, such as social capital (Field 2003) or institutional capital (Healey 1997). It can also be added that the relationship between the polarity and its environment has a multi-scalar character; on each occasion it can have relations just as well with the typical resources of the precise context as with the widespread resources of the urban or metropolitan environment, or at an even higher level. Moreover, this relationship has a biunivocal form: a polarity incorporates environmental features but at the same time develops and reproduces them, or, rather, consumes them, contributing each time to the sustainability or unsustainability of the development model it fits into.

Depending on the varying type of space considered, therefore, polarity shows itself as something different, though it is difficult just the same to imagine being able to completely do without one of the three dimensions studied. Above all, the relationship between polarity and city or metropolitan area seems very different for each of the three cases.

In the case of absolute space, this relationship is substantial: the urban system is only conceivable as a system of polar places; in relative space the city is put, so to speak, in second place: it is none other than a juxtaposition of related poles with flows whose size greatly surpasses the metropolitan dimension. Finally, in relational space we could say that city and polarity develop in a process of co-evolution with their environment; without taking into account this process neither one nor the other proves comprehensible.³