Wikipedia:Indexspam

Indexspam is the excessive use of indexing, such as having too many categories. There are many thousands of categories in the English Wikipedia, as people have created ever more subdivisions of subdivisions of prior categories from years earlier. In general, beware the creation of too many extra categories, and instead, consider discussions to delete the excessive categories and remove the category-links from the related pages.

To help avoid indexspam, develop a set of criteria, or index attributes, which can help to determine the appropriate sets of categories to support. In some cases, use of scientific techniques, such as factor analysis or cluster analysis, might help to identify the specific attributes where categories could be used, or else combined or deleted.