Geoscience Reference
In-Depth Information
The results of the clustering (Figure 3.10) highlight a first distinction between
two major groups of cities: those that are in relative growth and those which are in
relative decline (i.e. either in absolute decline or in a lower growth than the whole
system). This first major differentiation supports the hypotheses of a selection
process between the cities leading to the hierarchization of the urban system
[BRE 99]. This process benefits the cities at the top of the hierarchy, while most of
the cities that are smaller in size benefit less from the growth. Each of these two
major groups can be further subdivided, highlighting different time frames over the
four centuries. For example, regarding the class of cities with a relative growth, the
structure of the urban system is divided between the cities that have benefited from
the 19th Century growth (the large cities of the old industrial regions such as
Belgium, Germany, Holland), the cities whose growth has been continuous (France,
Germany and Italy) and those whose growth is recent (Mediterranean arc and
Eastern countries). The cities that are found at the interstices of this framework are
generally smaller at the end of the period, and have least benefited from the growth
over the whole period. The choice has been made to distinguish nine types of
trajectory. This division reveals that the relative growth or decline appear with
different intensities and temporalities. As an example, among the cities with low
relative decline (Figure 3.10), there are three types of trajectory:
- cities that have evolved the same way as the whole system;
- cities that have first lagged behind compared to the whole system's growth and
that have then been catching up with a growth stronger than the rest of the system;
- cities of which the start has been fast, but that have then seen some kind of
breathlessness compared to other cities.
This interpretation goes in the direction of the hypotheses expressed by the
authors, namely of a differentiated growth of cities due to a selection process. The
a
posteriori
mapping of the types of trajectory complements the graphics of average
trajectories of the classes with regard to the organization of potential interactions
leading to the hierarchization of the system.
3.3.1.2.
Evolution of economical specialization of American cities between
1970 and 2000
The second example appears as a complement to the first (methodologically and
thematically) by an analysis of the manner in which the cities adapt to economic
innovations: it concerns a longitudinal analysis on the economic specializations of
737 cities
8
of more than two million people in the United States described by the
distribution of the active population in 26 sectors of activities over four dates
between 1970 and 2000 [PAU 10]. The data is thus a typical case of the
8 Here, the city is considered with the meaning of the definition of “metropolitan area”.
