In order to help explain language variation and promote an understanding of spatial networks and diffusion patterns, data from the records of the Survey of English Dialects (SED) are analyzed with respect to geolinguistics. The data include all recorded instances of words with morpheme-final consonant clusters for all 75 interviews with older adult males made by the SED on the Isle of Man and in six northern countries of England. A variable rule for interpreting the data is analyzed, with a distinction drawn between the most restricted (or least general) version of the rule and the less restricted (or more general) versions. As these refinements of the linguistic analysis are mapped onto a spatial representation, a geographic correlate of the phonological analysis emerges: speakers with the more restricted versions of the rule tend to cluster together in areas which are bounded by the areas in which speakers with the more general versions of the rule are located. Attention is directed to the tendency to simplify morpheme-final consonant clusters in words (e.g., fist, post, bind, and thousand) so that they sometimes occur in speech as (fis', pos', bin', and thousan'). All speakers exhibited a tendency to simplify the final clusters. The phonological rule that underlies the linguistic behavior is examined. (SW)