Nodes of networks

In order to understand the specific meaning of networks it is necessary to clarify some definitions. Only when the underlying assumptions are made explicit can the concept be elaborated further. Assuming railway stations are nodes of networks, what do the terms 'node' and 'network' refer to exactly? In common parlance, a network is:

• a fabric or structure of cords and wires that cross at regular intervals and are knotted or secured at the crossings;

• a system of lines or channels resembling a network;

• an interconnected or interrelated chain, group, or system [as in a network of hotels].

(Webster's Ninth New Collegiate Dictionary, 1986)

A node is a point at which subsidiary parts originate or centre (ibid.). Together with 'lines' or 'channels' (or 'arches' or 'links'), nodes (sometimes called 'points' or 'vertexes') are the basic components of a network—the points where the lines are 'knotted', 'secured', 'interconnected' or 'interrelated'.

A crucial observation is that 'network' has both a concrete meaning (a fabric or structure of cords and wires) and a more abstract meaning (an interconnected or interrelated chain, group or system). This ambivalence can also be found in the use of the term in urban studies. Here the word has two basic connotations:

The first one comes from common sense and concerns infrastructure systems (highway and railway networks, drainage networks, etc.), the second one regards, lato sensu, the spatial interaction among urban places, economic activities and people. If the first one has a 'weak' meaning, describing rather than interpreting..., the second one offers, on the contrary, interesting metaphorical implications, but for this reason it seems difficult to use and to submit to an empirical validation. (Camagni and Salone, 1993, p. 1054).

In actual usage, the distinction made by Camagni and Salone is often not clear at all. Attributes of one connotation (that is, of infrastructure networks) tend, quite uncritically, to be attributed to the other domain (to socio-economic networks), or vice versa. Some positive impacts of the performance of, most notably, transportation networks on that of socio-economic networks seem apparent. Activities tend, for instance, to concentrate around transportation nodes such as airports, motorway outlets, or public transport interchanges. However, there are also activities that appear to be repelled by the same nodes, and nodes that do not seem to exert any attraction at all.

This confusion becomes particularly dangerous when we are studying railway station redevelopment. As major nodes of transportation networks, stations are often automatically equated with nodes of socio-economic activities. The Euralille venture, for instance, is founded on the hypothesis that 'the experience' of Europe is going to change radically under the double impact of the Channel Tunnel and the extension of the TGV network. If this hypothesis is verified, the city of Lille, centre of gravity of the London-Brussels-Paris triangle (30 million inhabitants), will acquire an immediate theoretical importance. It will become the seat of a number of typically modern activities. (Koolhaas, in Simon, 1993, p. 110).

While contentions such as this may contain an element of truth, they cannot be taken as anything more than a possibility. In any case, it must be established for which socio-economic networks a specific station is or may become a node, and under what conditions. In dealing with the problem, we shall use the terms 'network' and 'node' in their first connotation (the railway station as a node of transportation networks). Furthermore, we shall consider relationships, positive or negative, with their second connotation (the railway station as a node of socio-economic networks) as hypotheses to be verified, case by case.

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