This is a small project built during the Music Hack Day London 2014.
It uses Node.JS to access the Spotify Web API and stores data about artists' genres, popularity and follower count in a MongoDB database. Then, a script generates the data needed for the UI.
Have a look at the demo.
Note: Not every artist has been processed, but it's very likely that most followed/popular ones are in the dataset. Note that going through all artists involves a ton of requests.