Geography of languages deals with various aspects in areal distribution of languages: "the geography of languages assumes the history of the formation of the geographic area of certain languages, independent of linguistic phenomena proper... The field of the geography of languages is ... the study of present geographical distributions, determined by the expansion of languages and resulting from environmental conditions" (Delgado de Carvalho 1962: 75). Geography of languages spoken in Europe and North and Central Asia deals with the distribution of these languages in this large and complex area. This area is the geographical framework for the LENCA-project (LENCA <= Languages Spoken in Europe and North and Central Asia) which forms a framework for research of these languages and collecting information on these languages (cf. University of Helsinki Language Corpus Server).
Languages spoken in an area can be grouped into languages which have a long history in an area, "native languages", and into languages which are comparatively recent arrivals, "migrant languages". Migration and population transfers are continuously changing the areal distribution of languages and ethnic groups. The classification of languages into native and migrant languages is relative and vague: it may only take a generation for people who have moved to a new area to be considered native inhabitants of that area.
Delgado de Carvalho, C.M. 1962. The Geography of Languages. 75-93. In Philip L. Wagner and Marvin W. Mikesell (eds.). Readings in Cultural Geography. Chicago and London: The University of Chicago Press.