On the theories of Robert McCormick, blues historian:

"He investigated 888 counties before he was finished. He asked about everything, not just music but recipes, dances, games, ghost stories, and in his note-taking, he realized that the county itself, as an organizing geographical principle, had some reality beyond a shape on the map, that it retained in some much-diminished but not quite extinguished sense, the old contours of the premodern world, the world of the commons, how in one county you would have dozens of fiddle players, but in the very next county, none — there everyone played banjo. He began to intuit a theory of “clusters,” that this was how culture worked, emanating outward from vortices where craft-making and art-making suddenly rise, under a confluence of various pressures, to higher levels. "

From "The Ballad of Geeshie and Elvie" a New York Times article By JOHN JEREMIAH SULLIVAN

via longform.org