Geoscience Reference
In-Depth Information
- First step -
the potential exchange network
is composed of cities with which an
exchange could take place given the specialization of the city. These are cities in
close proximity in the case of the regional functions, or cities with strong functional
reciprocity in the case of specialized functions, such as finance.
- Second step -
the information exchange network
includes a selection of cities
among the previously mentioned. Following a double principle of
exploitation/exploration [MAR 91], consisting of valuing what is already acquired
and exploring in parallel new ways to innovate, the network is made up of part of
the city-agents that emerged as the best customers during the previous steps and a
set of cities randomly drawn inside the potential network. The cities being,
simultaneously, producers and consumers of goods and services, a multitude of
entwined exchanges take place.
- Third step -
the network of effective transactions
emerges from the set of
information exchanges between the city-agents corresponding to the second step.
Each city agent looks to sell its production to satisfy its demand in a context where
exchanges are intertwined, reflecting the competition between the cities. The
effective transactions are reflected by a transfer of wealth.
The period 1950-2000 was used to calibrate the main parameters of the model by
comparing the values of simulated and observed macrogeographical indicators
(evolution of the total European population and its rank-size organization in
particular). An informal sensitivity analysis
14
has been made through numerous
simulations. Scenarios were then developed to explore the effects of two kinds of
policies on the evolution of the European urban system up until 2050: (1) according to
the degree of opening of the European borders with regard to the immigration from
outside Europe; (2) according to the existence or non-existence of economic barriers
between the blocks of the Eastern and of the Western European countries [MAT 08].
Therefore, four “extreme” scenarios have been defined as:
1) a double opening, defining a context of demographic growth and free
economic exchange between Eastern and Western European cities;
2) an opening to immigration, with the associated demographic growth but
within a context of economic closure between Western and Eastern Europe;
3) a closure to immigration, with the associated demographic decline, but a free
economic exchange between Eastern and Western cities of Europe;
4) a double demographic and economic closure.
Figure 4.9 illustrates the ability of the model to produce different trajectories: the
artificial city (
L
), a great metropolis with many specializations at the international
14 A large number of simulations corresponding to different sets of parameters have been
carried out, but these simulations have not given rise to systematic replications.
