Researchers from the Polish Academy of Sciences have created a cartometric map to indicate the places drawn from ethnographic and folklore sources linked to demonic and mythological creatures.
What an interesting and novel way of presenting this information. It's interesting that the Will O' Wisp stories all cluster, while the others are much more spread out.
If I had the means to do folklore research on a full-term basis (and maybe a few research assistants as well), then this would be the kind of project I'd love to tackle for German folk tales.