The paper focuses on the geolinguistic treatment of demographic data, and more specifically of data elicited in multilingual settings. After establishing the basis of this chapter by briefly situating and differentiating geolinguistics and demolinguistics as subdisciplines of linguistics, we turn to a discussion of the kind of demolinguistic data on which a geolinguistic analysis is based and a brief presentation of the instruments (censuses, polls, and surveys) that are commonly used to gather such data. The final section homes in on the geolinguistic treatment of demolinguistic data by means of language maps.