NANCY Seminar – Zéphirin NGANMENI (Université Paris 8)

Event details :

Title: The Constitution in the Map: Evidence from Three French Metropolises

Abstract: Traditional power indices offer elegant measures of influence in collective decision-making bodies, but their foundational assumption of voter symmetry overlooks the critical role of geography in shaping political alliances. This limitation is particularly acute in metropolitan councils, where territorial interests and spatial proximity are paramount drivers of coalition formation. This paper challenges the symmetrical paradigm by arguing that the spatial configuration of member municipalities is not a passive backdrop but an active, constitutional determinant of power. Using a spatial voting game framework and a generalized distance-based power index, we analyze the distribution of influence within France’s three largest and most structurally diverse metropolitan councils: the monocentric Greater Paris, the bipolar Aix-Marseille-Provence, and the polycentric Metropolis of Lille. Our findings reveal a systematic divergence from the power distributions predicted by classical models. In Paris, centrality amplifies the core’s power; in Aix-Marseille, the eccentric position of the demographic heavyweight critically weakens its influence, breaking a formal dictatorship; and in Lille, the polycentric layout fosters a more balanced and negotiated distribution of power. The results demonstrate that a council’s political constitution is written as much in its territorial map as in its formal statutes, with a clear “geometry of pivotality” governing outcomes. This has profound implications for institutional design and public policy, revealing that major infrastructure and planning decisions are inherently political acts that redistribute power and offering a predictive tool for designing more equitable metropolitan governance.