The Music Timeline shows genres of music waxing and waning, based on how many Google Play Music users have an artist or album in their music library, and other data (such as album release dates). Each stripe on the graph represents a genre; the thickness of the stripe tells you roughly the popularity of music released in a given year in that genre. (For example, the “jazz” stripe is thick in the 1950s since many users’ libraries contain jazz albums released in the ’50s.) The Music Timeline is based on album and artist statistics aggregated from Google Play Music — popularity is defined by how many users have an artist or album in their music library.
Music timeline graph is an outstanding example of data Analytics powering data visualization, given the unique type of data needed to generate this graph, which only google has access to “Google play music” is a new type of data repository of user preference and user behavior.
It is not different than the data collected on usage of Cellphones by 98% of US population, the biggest sector of cellphone users.