4. An Incremental Multi-Modelling Method to Simulate Systems of Cities’ Evolution

Explaining the evolution of urban systems at large spatio-temporal scales is uneasy. Processes are frequently unobserved empirically and equifinality is a challenge for any generative explanation models. We try to address the causation challenge in urban modelling by proposing a multi-modelling framework for the comparison of several model structures. Each structure represents a combination of mechanisms translating alternative or complementary hypotheses about the processes at play. This approach implies that the conception, implementation and evaluation of the model(s) integrate a diversity of mechanisms. Their contribution to the explanation of urbanization is evaluated in time and space by confronting models to empirical data through an interactive visualization platform. We argue that multi-modelling can provide an alternative way to account for the possible causes generating observed patterns, between traditional approaches such as 1/simple models focusing on a single cause (as is often the case for proving a theory) or 2/very complex models including all possible mechanisms at once (as it might prevent from distinguishing their individual contribution).