Dialectology (from Greek διάλεκτος, dialektos, "talk, dialect"; and -λογία, -logia ) is the scientific study of linguistic dialect, a sub-field of sociolinguistics. (wikipedia)
Wikipedia: Dialectology is the scientific study of linguistic dialect, a sub-field of sociolinguistics. It studies variations in language based primarily on geographic distribution and their associated features. Dialectology treats such topics as divergence of two local dialects from a common ancestor and synchronic variation.
Abstandsprache - In sociolinguistics, an abstand language is a language variety or cluster of varieties with significant linguistic distance from all others, while an ausbau language is a standard variety, possibly with related dependent varieties.
Language geography - Language geography is the branch of human geography that studies the geographic distribution of language or its constituent elements. There are two principal fields of study within the geography of language...
Dialectometry - Dialectometry is the quantitative and computational branch of dialectology, the study of dialect. This sub-field of linguistics studies language variation using the methods of statistics; it arose in the 1970s and 80s as a result of seminal work by J. S guy and H. Goebl.
Language survey - A language survey is conducted around the world for a variety of reasons.