Does anyone want to look up all the pages about nothing? If not then there is no need for CategoryNothing. Is there a need for CategoryLiterature if there is already a CategoryBooks? How can you tell? How do you know when a new category is needed, when an old one will do, when none is needed or which pages should go into which category?
Who uses categories? What are the stories? Will adding a category or adding a page to a category be helpful? Ask the user. The relevance of categories is based on the needs of the users of the categories.
Is the "user" of a category someone that uses the content, or someone that uses the categorized structure, (or neither/both)? A: Someone using the structure.
The simplest thing to do is not to add a category unless you've actually wanted to look something up in that category. By extension it makes sense to add a page to a category, not simply because they seem to belong there, but because you, personally, have found it to be interesting and you'd like to be able to find it again.
Once you have the experience of being the user of categories in hand you will have all the knowledge and justification you need to make modifications to the categorization scheme.
This is an excellent idea. The purpose of WikiCategories is to simplify the search for pages having a common theme. It is important to have a reasonable number of pages, probably between 5 and 500. Do not create categories that do not have at least the minimum number of members. If a category approaches the upper limit it is probably time to subdivide.
On some wikis this feature is called TopicMaps?.? Please don't add a new category unless you can find ten other pages that would fall into that category.
I believe that categorization is an entire branch of LibraryAndInformationScience?. Before you add a category to a page, please put yourself in the place of a librarian. Think about whether the category is appropriate to the item and general enough to help others find related items. One notion we should think about is that of a "controlled vocabulary". The LibraryOfCongress has a strict set of words that can be used for categorization. Limiting the possible search terms keeps one's search options manageable.
To help think like a librarian, consider this quote from WikiPedia:
S. R. Ranganathan, considered by librarians all over the world to be the father of library science, proposed five laws of library science. Most librarians accept them as the foundations of their philosophy:
These laws are (replacing "page" for "book", "wiki" for "library"):
One might even consider AutomaticExternalCategorization