This study examines the aggregate change of the Democratic Progressive Party's (DPP) expansion between Taiwan's presidential elections from a spatial perspective. We find that the expansion of the DPP exhibited spatial clustering from 1996 to 2000. Its growth was clustered in southern Taiwan in this period, creating a considerable stronghold in the 2000 presidential election. From 2000 to 2004, however, the hot spots of DPP expansion shifted to central Taiwan and exhibited relatively dispersed patterns. To explain the spatial variation of the DPP's expansion, we incorporate independent variables of income, education, and ethnicity into regression models. The result of non-spatial regression analyses reveals that demographic characteristics played a role in the DPP's expansion. After inserting a spatial lag term into spatial regression models, however, we find that the impacts of some demographic variables have been overridden by the neighborhood effect. This implies that in addition to social cleavages, some campaign mobilization efforts or the socialization of one's network in the context of a broadly defined neighborhood could also have prompted the regional variation of the DPP's expansion. Further research is required to specify the mechanisms that formed the neighborhood effect.