Cities are so complex that we constantly build models to represent them, understand them and attempt to plan them. Models represent a middle ground between the singular configurations of cities and universal theories. This is what makes them valuable and prone to circulate (between places, institutions and languages) and evolve to adapt to new ideas, local conditions and/or other models. When it comes to analytical urban models (i.e. analytical representations of cities developed to study or simulate part of their structure or dynamics), there is a lack of academic understanding regarding how context and circulation affect their content, use and interpretation. What happens to analytical urban models and their reception during their circulation across geographical and disciplinary boundaries? How have different academic disciplines interacted with, contributed to and been influenced by analytical urban models? What are the consequences of urban models’ mobility for our understanding of cities? In this article, we employ the policy mobilities framework to analyse the circulation of analytical urban models. We use six canonical models as case studies to determine how their assumptions came about and how these models have circulated across different domains of policy and application by using biographical information and model analysis. The first contribution of the article is to demonstrate by example that our hypothesis regarding the influence of context is consistent. We also show that highly transferable/mobile models share common characteristics relating to contingent factors such as their creators’ biographies, institutional context and the traditional markers of power relations.@en

Agglomeration economies are a persistent subject of debate in regional science and city planning. Their definition turns on whether or not larger cities are more efficient than smaller ones. Here, we complement existing discussions on agglomeration economies by providing a sensitivity analysis of estimated externalities to the definitions of urban agglomeration. We regress wages versus population and jobs over thousands of different definitions of cities in France, based on an algorithmic aggregation of spatial units. We also search for evidence of larger inequalities in larger cities. This paper therefore focuses on the spatial and economic complexity of the mechanisms defining agglomeration within and between cities.@en

Scaling laws are powerful summaries of the variations of urban attributes with city size. However, the validity of their universal meaning for cities is hampered by the observation that different scaling regimes can be encountered for the same territory, time and attribute, depending on the criteria used to delineate cities. The aim of this paper is to present new insights concerning this variation, coupled with a sensitivity analysis of urban scaling in France, for several socio-economic and infrastructural attributes from data collected exhaustively at the local level. The sensitivity analysis considers different aggregations of local units for which data are given by the Population Census. We produce a large variety of definitions of cities (approximatively 5000) by aggregating local Census units corresponding to the systematic combination of three definitional criteria: density, commuting flows and population cutoffs. We then measure the magnitude of scaling estimations and their sensitivity to city definitions for several urban indicators, showing for example that simple population cutoffs impact dramatically on the results obtained for a given system and attribute. Variations are interpreted with respect to the meaning of the attributes (socio-economic descriptors as well as infrastructure) and the urban definitions used (understood as the combination of the three criteria). Because of the Modifiable Areal Unit Problem (MAUP) and of the heterogeneous morphologies and social landscapes in the cities' internal space, scaling estimations are subject to large variations, distorting many of the conclusions on which generative models are based. We conclude that examining scaling variations might be an opportunity to understand better the inner composition of cities with regard to their size, i.e. to link the scales of the city-system with the system of cities.@en