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degradation and configuration of commercial networks) that determine if the system
is resilient or not. The author notes that such interaction effects are specific to a
complex system and that the MAS formalization is particularly adapted to explore it
[HEC 13].
The comparison between this model and those of the Pueblo and Anazasi
populations, mentioned above, is interesting. It illustrates that a same problem, that
of understanding/explaining the abandonment of a geographical area, can be
formalized by making different choices about the elementary entity, the households
in the case of the works of Kohler
et al.
on Colorado's Pueblo as well as those of
Axtell
et al.
on the Anazasi of Arizona, and the group level for the MAS developed
by Heckbert on the Maya. The first two favor a positioning in terms of
methodological individualism, and formalize the rational behavior of households
faced with their environment. The interactions that operate at this level are
considered as the driving interactions. In the case of the Maya, it is the interactions
between the groups, at the level of their settlement, which are regarded as being the
drivers.
In Kohler's as well as Heckbert's works, the concept of “network” is mobilized.
The set of exchanges within networks is assumed to be essential in the dynamics of
the settlement systems in both approaches. However, the
level
considered to
formalize the action is different. The following example allows us to explain further
how to formalize networking within a settlement system, this time in the case of a
system of cities.
4.3.4.2.
The EuroSim model: simulating the dynamics of the system of European
cities between 1950 and 2050
The objective of the EuroSim model [MAT 08, PUM 09, SAN 10] is to explore
the role of trade among cities in their respective evolutions over a period of a
century, from 1950 to 2050. The initial situation corresponds to urban Europe in
1950, which is already highly structured. The objective is to identify the
mechanisms necessary to ensure that the urban structure in place is maintained or,
on the contrary, transformed (transition to a more polycentric organization, for
example).
The “city-agents” have attributes (population and economic specialization) and
have two roles. On the one hand, they are producers of goods and services that will
be offered within their networks of exchanges, on the other hand, they are
consumers of goods and services produced by other city-agents. At each time step,
each city-agent constitutes a network of exchange for each of its economic
specializations. The construction of these networks in three stages is one of the
distinctive features of the approach:
