What you're describing is an "isogloss." The linguistic atlas projects (U.S., Hans Kurath, 1930s) showed that certain forms and pronunciations could be mapped with amazing clarity, and the trends might reveal very old settlement-patterns, migration and trade-routes, or subtle geographic dividers. It's not that people stay in the same place so much as language is a naturally chameleon-like behavior -- we have strong tendency to norm to whatever pepole are doing around us, even if we regard it as "wrong." Do I remember correctly hearing that A5 was once a Roman road?

Music and stories once could be mapped in a similar way, but not many researchers today have the resources for that kind of fieldwork, or even an interest in the historic-geographic method. And I doubt the results would be anywhere near as dramatic, given today's distribution through electronic media.

Adam