This page sets out this wiki's principles of categorisation.

Ideally, every category except the top one should be a subcategory of at least one other category, and every article should be in at least one category; many will fit well into two (eg location and subject-matter). A full list of existing categories can be found at Special:Categories.

To add a new category, just add [[category:categoryname]] to the article or existing category page (after checking whether any existing category is suitable).