Categories In A Nutshell
Opinions vary regarding on how to use WordPress Categories. But, this SEO blog has pretty firm opinions regarding categories. Categories should never be indexed.
Do NOT Index Categories
Categories are a feature of WordPress blogs. They exist for the benefit of visitors to your blog. They contain no original content and, thus, are nothing but duplicate content. On WordPress blogs original content exists only on individual posts and pages.
Categories Change Frequently
Furthermore, the URLs of categories as well as how you have classified individual posts on your blog are subject to frequent changes, especially for a new blog. Just like tags, there is absolutely no reason why you cannot change your category classifications on the fly. Thus, if your categories are indexed trying to keep up with URL changes, with 301 redirections, can be quite a headache; if not a downright nightmare. And, you certainly do not want your categories being part of the permalink structure for posts for similar reasons.
Design Your Categories As Hierarchies
Next, categories should express a hierarchy of topics. Just because most SEO blogs use a flat category structure, is totally besides the point. This SEO blog operationally shows how categories can be viewed as hierarchies. And, that setting up hierarchies with categories offers advantages over a flat category structure. As you experiment with different category classification schemes that captures topics differently, you are all the more likely to make major URL changes.
Categories Are Hierarchies of Topics
With hierarchies, you assign posts to categories at the lowest level. Automatically, the post is also included in every category that is hierarchically listed above it. Further, hierarchical categories illustrate how different topics are related to each other. These are the advantages of designing your categories as hierarchies.
Do NOT Follow Categories
Finally, a hierarchical category system goes around in circles linking to the same posts over and over again. Thus, in order to avoid a maze of circular links you should also be using a WordPress plugin that automatically places a nofollow tag on all category hyperlinks.
