isoglosser

An isoglosser is a person who identifies and maps isoglosses, lines on a map that mark the geographical boundary of a linguistic feature. The term isogloss comes from Greek isos meaning equal and glossa meaning tongue, with the suffix -er indicating a practitioner. In dialect geography, an isoglosser collects data from speakers—phonological, lexical, syntactic, or semantic features—and determines where the feature is present or absent. By plotting multiple features, the isoglosser helps outline dialect areas and observe how language varies across space. Isoglosses can be single lines or sets that intersect and form complex boundaries.

Data quality and sampling influence isogloss maps; small samples or biased data can create artificial lines. Features may be gradual rather than abrupt, producing fuzzy boundaries known as gradual isoglosses in some descriptions. Isogloss mapping is a foundational method in dialectology and sociolinguistics, complementing deeper statistical analysis and fieldwork. While the term isoglosser is used informally, more common descriptors include dialectologist, linguistic cartographer, or isogloss mapper.

Examples of isoglosses include lexical boundaries such as the distribution of words like soda versus pop, or regional pronoun forms, where communities differ in usage. In practice, an isoglosser works with existing maps or geographic information systems to present a visual representation of language variation and to formulate hypotheses about historical language contact and regional development.