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Analysing and Modelling the Geographical Diversity of Cities and Systems of Cities

Final Report Summary - GEODIVERCITY (Analysing and Modelling the Geographical Diversity of Cities and Systems of Cities)

The evolution of cities is a major issue because it affects the majority of the world population. It is in cities that solutions must be invented to solve the problems of sustainable development in terms of quality of life, of resource management, of intelligent integration of technological and cultural innovation and of social cohesion, at the local and the global scales. The diversity of cities is such that it might seem difficult to develop a scientific knowledge about them. However, cities have long been interdependent and organised into systems of cities, they co-evolve through the multiple relationships which connect them into networks for the exchange of materials, investments, people or information. These interdependencies drive and constrain the evolution of each city in the system, according to a complex set of dynamics which exhibit patterns regular enough to help understanding and even predicting certain trends.
The objective of the GeoDiverCity project was to test our knowledge about this dynamics, formalised in an evolutionary theory of urban systems, by developing an original research strategy. The methodology combines empirical statistical observations with analyses inspired from the dynamics of complex systems, integrating data and processes into computer simulation models which are able to reconstruct the stylized facts and trends observed. The strength of the theory has been tested on a variety of cases in seven world regions including the BRICS, Europe and the United States, over long periods of time: from several decades to several centuries, thus covering more than 20 000 cities and towns with a population ranging from 10,000 residents to 30 million. The results confirmed the importance of interactions between the cities in the evolution of their size and the effects of the spatial diffusion of large innovations waves, which tend to reinforce the hierarchical unevenness and explain the reversal of trajectories in the specialized cities. The path-dependent role of the precocity and sustainability of settlement systems is confirmed as well as the bifurcations associated with colonisation in creating a diversity of systems of cities in terms of hierarchical inequality and the primacy of their metropolises. The evolutionary theory also proved to provide a rich and significant interpretation of urban scaling laws which are currently under the radar of scientific debates.
The project has established a strong interdisciplinary collaboration of the win-win type between geographers and computer scientists. The project has succeeded in generating major achievements that are " exported " to other laboratories and disciplines of the humanities and social sciences : 1 ) creating an entirely new methodology for the validation of social science simulation models through a full exploration of their parameter space (using genetic algorithms and grid computing) ; 2) proposing an incremental method for model building based on a ranking of their dynamic mechanisms and contextual elements that diversify the paths of cities ; 3 ) contributing to the development of the OpenMOLE platform which enables free, repeatable and reproducible experimentations of these complex models.
In terms of structuring a research space, the project supported a remarkable upscaling of the laboratory skills in terms of modeling capability and has established many links between the social sciences and other disciplines dealing with complex systems. It has consolidated important research networks on complex systems, nationally and internationally, bringing together geographers, mathematicians, physicists and computer scientists. This teamwork has contributed to the success in the career of its members: 7 doctors were supervised and defended their PhD with honours; after the project four people hold permanent research positions and five people have been appointed as post-doctoral research fellows abroad. Another important success of the project is to illustrate the capabilities and effectiveness of an open science.