This paper introduces a technique for exploring regional linguistic variation, identifying individual and common spatial clustering patterns in a series of linguistic variables measured over a range of locations based on a combination of three statistical methods: spatial autocorrelation, factor analysis, and cluster analysis. This method is then employed to analyze regional variation in the values of 40 lexical alternation variables in a 26-million-word corpus of letters to the editor, representing 206 cities from across the United States.