Each page in the Category namespace represents, lists, and perhaps defines a category, or grouping of related pages. Categories place pages on related topics in one "container." A category page on Wikipedia should offer an overview of the coverage of a particular subject. How extensive is the coverage? How are articles organized? Is the particular topic you want there, but under a title that wouldn't be your first choice? Is there a subcategory that's a better fit for the area you want to research?
You learned how to navigate with categories in "Browsing by Categories" on Section 3.4, “Browsing by Categories”; in this section, you'll learn how to use them as an editorial tool.
All articles should be in at least one category; most articles are in more than one category. Some areas are particularly important to categorize: For instance, work is ongoing to track all Wikipedia's biographies of living persons in [[Wikipedia:Living people]], with the number of articles running well into the six figures.
When an article is in one or more categories, this information appears at the very bottom of the article in an automatically generated section called Categories.
Clicking any category link will take you to the main page for that category. As described in Chapter 3, Finding Wikipedia's Content (see Figure 3.10, “Example of a category page (the category of Fictional Countries), showing editable sections” on Section 3.4.1, “Structure of a Category Page”), a category page has four parts:
The explanation of the category; this text (along with the category's discussion page) is editable and is what you'll see if you click Edit This Page.
A list of any subcategories within the category; these are listed alphabetically, but if the category is very large, the list may be spread over several pages.
A list of links to articles in the category; this list is automatically populated. If the category is very large, the listing may be spread over several pages; only the first 200 links will appear on the first page. Click Next 200 at the bottom of the page to see the next page of entries.
At the very bottom, you'll find a list of the categories that the category you're viewing is part of. These are editable by editing the category page.
You can assign a page to any category simply by adding
[[Category:categoryname]]to the page's wikitext. Substitute the actual name of the category in place of categoryname.
For example, to add the article [[Bozo the Clown]] to the Clowns category, you would edit the article and add the text [[Category:Clowns]] at the very bottom of the page.
Placing an article in a category by adding a category tag does two things:
It automatically lists the article on the appropriate category page.
It also provides a link to that category page in the list of categories at the bottom of the article.
Though no connection exists between the location of the category tag in the article source text and where the Categories box appears on the page, the general convention is to place categories together at the end of the source text (though before any interwiki links), one per line, so they don't affect the rest of the text and are all in one place. (Figure 8.5, “Article wikitext with multiple categories listed near the end of a page (after templates and before interwiki links), from the article [[Exploding whale]]” shows the placement of categories in an article's wikitext.) Wikipedia has no standard order for categories.
Figure 8.5. Article wikitext with multiple categories listed near the end of a page (after templates and before interwiki links), from the article [[Exploding whale]]
![Article wikitext with multiple categories listed near the end of a page (after templates and before interwiki links), from the article [[Exploding whale]]](resources/wiki08_05.png)
Articles can be included in more than one category by adding multiple category tags. For example, for a person no longer alive, the standard categories are year of birth, year of death, and occupation. Most articles are naturally in more than one category.
To link to a category in wikitext without categorizing the page, type
[[:Category:Instruction]]
Doing this is useful for See also sections in articles. This is also vital if you want to discuss a category on a talk page. If you leave out the first colon, the text of the link won't be displayed, and the page will be categorized in that category.
Like everything else on Wikipedia, categories are not canonical. Sometimes they are even incorrect or misleading, usually as the result of an honest mistake. Articles should be placed in categories simply to inform, never to make a point or forward a controversial position. Obviously, if an article about a person is in a category damaging to his or her reputation, the classification should be fully supported within the article. No one should just add [[Category:Murderers]], unjustified, to a biography. Wikipedia doesn't allow its category system to be used as a way of commenting on content.
In general, anybody adding categories to an article should follow the same basic policies of Verifiability, No Original Research, and Neutral Point of View that govern the rest of Wikipedia. Categories are part of the informational content of an article and should be treated appropriately: They should be supported by references (or more properly by statements in the article's text that are themselves referenced), especially if the category is contentious. (One disadvantage of categories as opposed to lists: You can add sources to a list to support inclusion, but you can't annotate an article's categories directly.)
Wikipedia has many guidelines for categorizing articles; [[Wikipedia:Categorization FAQ]] is one place to find them. [[Wikipedia:Categorization of people]], another guideline, explains the sensitive subject of placing people in categories that might affect their reputation. Especially for biographical articles about living people, use caution when adding categories other than very formal and descriptive ones.
You can start a new category easily. If you add a category to an article, but the category doesn't exist yet, it displays as a redlink in the article's list of categories. To turn the redlink blue, simply click it (or visit [[Category:New category name]], where new category name is the category you want to create) and add some content, such as a brief description of the category and the categories it is a subcategory of, to the category page. Any pages that you or others have already tagged with your new category name will automatically be listed on the new category page.
For example, [[Category:Poisoned apples]] could be created by adding this text to the new page [[Category:Poisoned apples]]:
A poisoned apple is an apple that has been poisoned. [[Category:Apples]] [[Category:Fairytale objects]]
The description will appear at the top of the category page, and adding the categories will instantly make poisoned apples a new subcategory of the Apples and Fairytale Objects category.
All new categories should have their broader categories listed, but including a description is optional; in this case, the description isn't very helpful. In some cases, though, a good description (perhaps linking to the main article on the subject) will help the average reader, especially for obscure subjects.
Wikipedia also has naming and structural conventions for creating categories. Use plurals, for example [[Category:Pigs]], for categories. This convention differs from the article title convention of generally preferring the singular form. Proper names such as [[Category:Vermont]], which collects articles about the state, or collective headings such as [[Category:Greek mythology]] are also common category names.
Before creating a new category, make sure the category you want doesn't already exist under a variant name (check articles similar to the one you're trying to categorize). Creating categories that are not obviously needed is considered a nuisance.
Categories can have subcategories. Anyone can create or alter subcategories by simply categorizing the category page. For instance, you could make [[Category:Piglets]] a subcategory of [[Category:Pigs]]; simply tag the [[Category:Piglets]] page with [[Category:Pigs]]. Using the subcategory and supercategory structure is a good way to browse the site and is discussed extensively in Chapter 3, Finding Wikipedia's Content.
Here, we'll discuss the issues around classifying articles using detailed categories. Are detailed subsubcategories a good thing or not? Certainly having categories that contain too many articles can be unwieldy; a category with more than 200 articles in it requires multiple pages. Subcategorizing the articles into more distinct categories can help keep categories manageable.
Subcategories are useful on Wikipedia to subclassify when the schematic being followed is fairly natural to the subject matter and the relevance is evident. [[Category:Politicians with blue eyes]] is not helpful—why would anyone be looking for this information? But [[Category:Canadian buskers]] is an acceptable subcategory of [[Category:Buskers]] or of [[Category:Canadian musicians]]. Subcategories should offer the general reader a convenient way to navigate a category and also provide information about the material included in a category.
Following a general but not quite universal convention, articles should not appear in both a category and a subcategory. For instance, [[Category:Beetles]] within [[Category:Insects]] classifies some insects more precisely. According to the convention, the beetle articles should not also be in the more general [[Category:Insects]]. Therefore, in searching [[Category:Insects]] for all the Wikipedia articles on insects, you would also have to search [[Category:Beetles]] and, within that, more than a dozen subcategories to find all of the beetle pages. Going through all the subcategories is the only comprehensive way to find all the articles related to a larger category, such as insects; if in this case you went to the page [[List of insects]], you'd discover this list is a redirect to [[Category:Insects]]. While finding all Wikipedia articles about insects is probably unreasonable (as the category is enormous), creating extremely detailed subcategories for smaller topics can make it difficult to see all the related articles at a glance. On the other hand, articles should always placed in the most detailed category that applies: An article about a beetle found in New Zealand should be placed in the Beetles of New Zealand category, not the higher-level category Beetles.
You can find lots of information about projects to improve the use of categories at [[Wikipedia:WikiProject Categories/Current subprojects]]. You can also find an overview at [[Category:Wikipedia categorization]].
One long-standing categorization project that crosses all disciplines is [[Wikipedia:WikiProject Stub sorting]]. This project maintains the article categories for stubs, a list of which can be found at [[Wikipedia:WikiProject Stub sorting/List of stubs]]. These special categories are applied to articles not with standard category tags but with templates, which are discussed in the next chapter.