In moderate US districts where political parties switch hands, state legislators' behavior reflects the district's diverse voter ideologies. Our analysis shows that when voters are heterogeneous—like in areas with both liberal cities and conservative rural regions—the ideological gap between Democrats and Republicans is wider than expected.

To explain this finding, we developed a formal model linking intradistrict heterogeneity to uncertainty about the median voter ideology. This model suggests that legislators face greater challenges predicting public preferences due to varied constituent views.

We then demonstrate empirically that among districts with similar median voter ideologies, legislative polarization is stronger in those with higher internal ideological diversity. Our findings highlight how accounting for political geography helps reconcile seemingly moderate electorates with polarized policy outcomes.