The Essen folksong collection is an intriguing relic of computational musicology. With its origins clad in a veil of mystery , it is used widely as an empirical source of symbolically encoded folk melodies.
Along with each melody, some information on its likely geographical region of origin is provided. This information, though meticulous, is a bit tangly.
This visualisation is based heavily on this Github gist.
Some related resources:
- The Essen folksong collection in humdrum format at KernScores
- An (web-archived) explanation of the humdrum “reference records”, which contain metadata such as region of origin
 In a footnote in his book Music and probability, David Temperley writes: “Unfortunately, very little is known about how the corpus was created: the method of gathering the data, when and where it was gathered, criteria for inclusion, and so on. The project was supervised by Helmut Schaffrath, who provided very little public information about this before his death in 1994. […] It is believed that much of the data comes from published collections of folk songs (Eleanor Selfridge-Field, personal communication). The corpus also includes a large number of non-European songs, but these were not used in the current study.”