Dialect cluster

A dialect continuum or dialect chain is a spread of language varieties spoken across some geographical area such that each differs only slightly from its neighbors, but the differences accumulate over distance so that widely separated varieties are not mutually intelligible. That happens, for example, across large parts of India or the Maghreb. Historically, it also happened in various parts of Europe such as between Portugal, southern Belgium and southern Italy, and between Flanders and Austria. Leonard Bloomfield used the name dialect area. It is analogous to a ring species in evolutionary biology.

Dialect continua typically occur in long-settled agrarian populations, as innovations spread from their various points of origin as waves. In this situation, hierarchical classifications of varieties are impractical. Instead, dialectologists map variation of various language features across a dialect continuum, drawing lines called isoglosses between areas that differ with respect to some feature.

Since the early 20th century, the increasing dominance of nation-states and their standard languages has been steadily eliminating the nonstandard dialects that comprise dialect continua, making the boundaries ever more abrupt and well-defined.

Dialectologists record variation across a dialect continuum using maps of various features collected in a linguistic atlas, beginning with an atlas of German dialects by Georg Wenker (from 1888), based on a postal survey of schoolmasters. The influential Atlas linguistique de la France (1902–10) pioneered the use of a trained fieldworker. These atlases typically consist of display maps, each showing local forms of a particular item at the survey locations.

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