Scratchpad:Categories/Subcategories



If logical membership of one category implies logical membership of a second, then the first category should be made a subcategory (directly or indirectly) of the second. For example, Cities in France is a subcategory of Populated places in France, which in turn is a subcategory of Geography of France.

Many subcategories have two or more parent categories. For example, Category:British writers should be in both Category:Writers by nationality and Category:British people by occupation. When making one category a subcategory of another, ensure that the members of the subcategory really can be expected (with possibly a few exceptions) to belong to the parent also. Category chains formed by parent-child relationships should never form closed loops; that is, no category should be contained as a subcategory of one of its own subcategories. If two categories are closely related but are not in a subset relation, then links between them can be included in the text of the category pages.

A page or category should rarely be placed in both a category and a subcategory or parent category (supercategory) of that category (unless the child category is non-diffusing – see below). For example, the article "Paris" need only be placed in "Category:Cities in France", not in both "Category:Cities in France" and "Category:Populated places in France". Since the first category (cities) is in the second category (populated places), readers are already given the information that Paris is a populated place in France by it being a city in France.

Note also that as stub templates are for maintenance purposes, not user browsing (see above), they do not count as categorization for the purposes of Wikipedia's categorization policies. An article which has a "stubs" category on it must still be filed in the most appropriate content categories, even if one of them is a direct parent of the stubs category in question.

Diffusing large categories
Although there is no limit on the size of categories, a large category will often be broken down ("diffused") into smaller, more specific subcategories. For example, Category:Rivers of Europe is broken down by country into the subcategories Rivers of Albania, Rivers of Andorra, etc.

A category may be diffused using several coexisting schemes; for example, Category:Albums is broken down by artist, by date, by genre etc. Metacategories may be created as ways of organizing schemes of subcategories. For example, the subcategories called "Artistname albums" are not placed directly into Category:Albums, but into the metacategory Category:Albums by artist, which itself appears in Category:Albums.

It is possible for a category to be only partially diffused – some members are placed in subcategories, while others remain in the main category.

Information about how a category is diffused may be given on the category page. Categories which are intended to be fully broken down into subcategories can be marked with the catdiffuse template, which indicates that any pages which editors might add to the main category should be moved to the appropriate subcategories when sufficient information is available. (If the proper subcategory for an article does not exist yet, either create the subcategory or leave the article in the parent category for the time being.)

To suggest that a category is so large that it ought to be diffused into subcategories, you can add the verylarge template to the category page.

Non-diffusing subcategories
Not all subcategories serve the "diffusion" function described above; some are simply subsets which have some special characteristic of interest, such as Best Actor Academy Award winners as a subcategory of Film actors, Toll bridges in New York City as a subcategory of Bridges in New York City, and Musical films as a subcategory of Musicals. These are called non-diffusing subcategories. They provide an exception to the general rule that pages are not placed in both a category and its subcategory: there is no need to take pages out of the parent category purely because of their membership of a non-diffusing subcategory. (Of course, if the pages also belong to other subcategories that do cause diffusion, then they will not appear in the parent category directly.)

Non-diffusing subcategories should be identified with a template on the category page.
 * The Non-diffusing subcategory templates should be used for sub-categories that are non-diffusing, like.
 * The All included can be used for categories where all child articles of a certain type are in the parent, like or.

Subcategories defined by gender, ethnicity, religion, and sexuality should almost always be non-diffusing subcategories. The Categorization/Ethnicity, gender, religion and sexuality categorization guideline outlines the rules on these categories in more detail. Note that some categories can be non-diffusing on some parents, and diffusing on others. For example, is a non-diffusing sub-category of, but it is a diffusing subcategory of.