At the time of writing this, Spotify--the music subscription service, lists about 1,500 genres and subgenres of music. The site everynoise.com offers an entertaining experience for exploring Spotify's genres using an algorithmic visualization. The site musicmap.info provides a beautifully engaging and insightful presentation of the history of hundreds of popular music genres from the 1870s to the present. The site musicgenreslist.com, which claims to have "The most definitive music genre list on the web", has a more traditional display of genres organized in hierarchical clusters.

The problem is that in music, as with fashion, technology, food, and nearly all areas of content, it is getting very difficult to be definitive when it comes to classifying, grouping and organizing new information. Wikipedia lists over 80 shoe styles, New Balance lists nearly 70 shoe categories, and Samsung offers nearly 70 TV models differentiated by technology, series, and size.

Key aspects of a great experience design involve fast discovery and easy navigation, which is challenging with so many content category options. Figuring out how to create navigation and organize content for discoverability, is part of Information Architecture, a topic is described in more detail in Chapters 6, Design Disciplines. Card sorting is a technique that helps designers figure out content organization questions.