The aim of the model is :
To simulate the genesis of an urban system in Europe by
reconstructing the patterns of exchanges between them
To test hypothesis on the role of innovation and
communication speed in the emergence of hierarchical structure
Starting from the
generic model SIMPOP2, we test:
The effectiveness of the interaction rules for differentiating
size and functions of cities throughout seven centuries
The effect of previous geographical organization of the system
on its further dynamics (path dependence) by comparing a real and
a geometrical initial situation (figure 1).
About 400 simulations have been run.
1- Estimation of historical parameters
Historical databases on population statistics have been worked out
from existing ones (Bairoch and al. 1988, Moriconi-Ebrard 1994) by
applying a strict methodology for comparison through time (evolutionary
definitions of urban agglomerations then travel to work areas).
From other sources, we have extracted benchmark statistics regarding
urban wealth and urban functions (Maddison, Bairoch, Braudel,
Mitchell, Pinol, de Vries...).
Key parameters (productivity, demand, labour force, spatial range per
function) were first roughly estimated from available sources then
refined through calibration. The variations were kept consistent with
principles of urban theory.
2- Calibration method
Calibration has been made iteratively across levels, on total figures
(population and wealth), city size distributions, distribution of labour
force, types of cities trajectories (figure 2).
Major changes in key parameters have been made to reproduce the main
inflexions on evolution curves :
Two distinct dynamical regimes (before and after Industrial
Revolution) have been identified, involving two different orders
of magnitude in parameter values (see Table 1)
General but temporary events as the Black Plague (14th century)
or the pre-industrial recession (18th century) have been generated
by momentary changes in key parameters.
3- Role of endogeneous and exogeneous interactions in shaping the urban system
The rules of the model are sufficient for generating the major part
of cities trajectories but they fail in reproducing the specific size
of the largest metropolises (table 2).
Those cities had an exceptional growth because of their "international"
This led us to inject a new function in the model, that is called
world-city function. This function supplies an external demand by addressing
it to other urban functions and levying part of the induced wealth. This
function was revealed as a necessary ingredient of the model, as early
as Middle Age (much before the general acknowledgement of "global cities"),
and not only for simulating these exceptional cases in Europe but also for
simulating "ordinary" urban growth in new world countries (United States).
The EUROPEAN LONG-TERM model was developed in the framework of
ISCOM (European project directed by David Lane)