Abstract : Focused on the French case, this paper aims at investigating a geographical change of electoral support, which is part of wider transformations of the electoral base of the Socialist Party, in particular the trend of working class dealignment. While a specific sociology emerged in "ideopolises", anchored in the post-industrial and knowledge-based economy, a shift of the traditional socialist electoral support occurred in those cities (but not for all types of elections). We argue that this dynamic has been particularly pronounced in 2007.