Before revision: Partisan sorting or geographic sorting is an effect in politics in which voters with specific viewpoints migrate to specific areas, becoming much more concentrated in them than in the wider electorate.This effect may create or contribute to an effect of polarization, in which separate areas become dominated by political movements much more extreme than might be expected given the sort themselves into parties that match their ideology.
After revision: Partisan sorting is an effect in politics in which voters sort themselves into parties that match their ideology.