Final answer:
Linguistic geographers use isoglosses to mark linguistic boundaries and variations.
Step-by-step explanation:
Linguistic geographers use isoglosses to mark linguistic boundaries and variations. An isogloss is a line on a map that separates areas where a particular linguistic feature is present from areas where it is not. These features can include pronunciation, vocabulary, and grammatical structures. Isoglosses help linguists identify dialects and language variation within a region or across different regions.