@An example on a tagging effort gone off the rails (started out interesting):
https://flipboard.com/htmlsitemap/popular/1
3 years or so ago, Flipboard had 400+ #topics / #tags, even for a normal, non-tech audience(s).
This illustrates the challenge of "#categorisation" quite well.
Even though far too many of them are not even proper "topics", if you focus on those that in fact serve their purpose, this is not a bad #resource for this kind of #research / #analysis