Wikipedia:FAQ/Categorization

Categorization FAQ

Frequently asked questions about the Wikipedia Category feature.

For a quick introduction to using categories within articles, see Help:Category. For guidelines on creating and organizing categories, see Wikipedia:Categorization.

What are categories?

Categories allow articles to be placed in one or more groups, and allows those groups to be further categorized.

When an article belongs to a category, it will contain a special link to a page that describes the category. Similarly, when a sub-category belongs to a parent category, it will contain a special link to the parent category's page.

Each category page contains an introduction that can be edited like an article, and an automatically generated list of links to sub-categories and articles that belong to the category.

Categories do not form a strict hierarchy or tree of categories, since each article can appear in more than one category, and each category can appear in more than one parent category. This allows multiple categorization schemes to co-exist simultaneously. It is possible to construct loops in the category space, but this is discouraged.

What is the purpose of categories?

There are two main ways to use categories: lists and topics. When starting a subcategory, making an early decision about whether it is a list or a topic will reduce later renames, recategorizations, and discussions. The category page can be used to tell others whether it is a list or a topic, and to link to a main list or article in the main, article namespace.

See meta:Categorization requirements for the original purpose of the feature, and Wikipedia:Categorization for current usage and guidelines for assignment.

What categories already exist?

The best way to find out what exists is to browse. Either start at Wikipedia:Browse or start at Category:Fundamental, which shows the "top" level categories, to which all other categories should be connected. Category:Categories is the standard top-level category provided by the MediaWiki software, but orphan categories (categories without any parent categories) can exist. Category Tree browser at the Toolserver is a javascript category browser. Cat Scan, also at the Toolserver, can be used to find subcats.

Wikipedia:Category schemes shows designs that predate the category feature. Some high-level categories can be found at Wikipedia:Categorization#Current projects. A list of all categories can be found at Special:Categories, but it is not very useful since there are many thousands of categories listed there.

How else can I navigate articles?

As well as the standard links within articles themselves, every page has a link (typically at the side) called What links here.

What is the difference between a list and a category?

Grouping articles into a category is not the same as making a list of articles. When you make a list of articles, you edit the list directly; but when you place articles into a category, you simply edit the articles, and a list of articles is automatically created on the category's page. Despite the difference in how they are maintained, it is sometimes convenient to think of a category as a list of articles.

While an article may be in multiple lists, the goal is that browsing downwards from a list parent category, e.g. Category:Cities, should only arrive at articles that are cities, e.g. London, and not related articles e.g. History of London. See the John Lennon example.

There are some natural hierarchies of lists. One example is the scientific classification of organisms, which would only place an article in one category. Other systems use multiple listings, e.g. Wikipedia could be in Category:Wiki and Category:Encyclopedias.

List categories are likely to also be subcategories of topic categories.

Maintaining and tracking categories often requires more effort than a simple list. If you have a category that has vague criteria or that adds and removes members frequently, then maintaining a simple list is often more appropriate.

Further information on this topic can be found at Wikipedia:Categories, lists, and series boxes.

Are "List of ..." articles still needed?

There are many articles in Wikipedia called "List of ...", e.g. "List of assassins". Lists are still useful for showing "missing" articles. See also: Wikipedia:Categories, lists, and series boxes, Wikipedia talk:Categorization/Archive 1#Lists v. categories and Category:Lists that should be categories.

Are topic and hierarchy info-boxes still needed?

Many articles have "info-boxes"—side-boxes or footers linking to other articles and lists, sometimes using Wikipedia:Templates. Some of these are listed at Wikipedia:Navigational templates. While some info-boxes are made redundant, others have useful grouping of the cross-references that cannot be done with categories. See also: Wikipedia:Categories, lists, and series boxes, Wikipedia:Article series, Wikipedia:Incumbent series.

Can pages be in more than one category?

Yes, it is expected that most pages will be members of more than one category.

In exactly the same way, each category can be a member of more than one parent category.

What is the naming convention for categories?

Use the Wikipedia titling conventions of no unnecessary capital letters or abbreviations, i.e. use [[Category:Category examples]] instead of [[Category:Category E.g.]]. Avoid ambiguities.

Lists

If the category is used like a list of articles, then avoid the word List in the name of the category, and use plurals, e.g. Category:Popes.

However, if the category is used like a list of lists, then using the word Lists in the name of the category is appropriate, e.g. Category:Lists of radio stations.

Topics

Use the topic name without indicating structure, e.g. [[Category:History of London]] instead of [[Category:History - Europe - UK - London]].

Editing articles

How do I add an article to a category?

Edit the article and add [[Category:Category name]] at the bottom of the article.

How do I reference a category on a page without categorizing the page?

To link to the category page, put a colon before the word "category", inside the link, e.g.
[[:Category:USA]]. The link will appear as, e.g., Category:USA.

Where should the category tag go in the article?

Category tags should be placed at the bottom of the article, after the appendices and before the inter-wiki language links. This ensures that when newcomers press "edit", they are immediately presented with the main article text, rather than the more esoteric category tags. It also ensures that the category tags are in a consistent place so they are easy to find when an editor is updating the categorization of a bunch of articles.

In what order should categories be listed within the article?

The obvious options would be by importance, or possibly alphabetically. While the former seems to be the general practice, I've found no explicit recommendation within help pages - the only mention of this at all is "There is currently no consensus about the order in which these categories should be placed at the bottom of an article." at Wikipedia:Categorization of people#Categorisation schemes. --Malyctenar 11:43, 26 October 2006 (UTC)[reply]

How do I sort the article differently on the category page?

This is needed especially for sorting people by surname, leaving out articles ("The" and "A") from the beginning of names, and other cases when preferred sorting key is not identical with article name; Such as grouping people with surnames starting with 'Mac' and 'Mc' together, or to force the most important articles or sub-categories to appear at the beginning of the list.

In such cases use the "pipe-trick": Expand the category notation to include the desired sorting key after a pipe sign (syntax is similar to Wikipedia:piped link, but the effect is different). For example, an article categorized by [[Category:Proper category|''Sorting key'']] would appear under S within the category.

See thorough manual at Wikipedia:Categorization#Category sorting.

Which categories can be used for categorization of articles on people?

Articles about people should be categorized cautiously. Unlike the body of the article, the various category choices for people can focus on what, in most cases, are common and unrelated attributes such as place of birth and gender, instead of emphasising the reason for their inclusion.

See Wikipedia:Categorization of people for guidelines.

Somebody changed my categorization - what do I do?

All contributions to Wikipedia may be "edited mercilessly". If the change was not explained in the article history or talk page, try leaving a question on the relevant user's talk page.

What should I do if I see an article without any categories?

The easiest way to handle it is to add the {{Uncategorized}} template to the article, which will place a notice that the article needs categorizing, and automatically add it to the list at Category:Category needed. Or, try to categorize it yourself. One useful technique is to try following links in the article to other similar pages, and see how they are categorized, so you know what to copy.

Maintaining categories

I am interested in XYZ categories - where can I get involved?

See Wikipedia:Categorization#Current projects, Wikipedia:WikiProject and Wikipedia talk:Category schemes.

I want to change the relationships of some categories - will anyone mind?

If you want to restructure some existing categories, it is best to discuss your plans with others working in the same areas, or at least to announce your intentions. This is to avoid the situation where someone is placing an article into multiple categories, someone else is populating a category with multiple articles and parent categories, while someone else is trying to restructure part of the category tree, and nobody ends up with what they want. A good place to start looking for an interested group of people is Category:WikiProjects.

What goes on a category page?

Category pages exist to be a convenient cross-reference to related articles and other categories. A category page should contain a brief description of the purpose of the category. A prominent link to the most important article in the category is usually a good idea, but please avoid copying large quantities of text or images from an article to a category page. If a category and a page have a one-to-one correspondence, then the template {{catmore}} or similar is often the best solution.

The {{catmore}} template

In many cases, a category has a "main article", which describes the subject of that category. The category and the article often have the same name. In such case, do this:

Add the "{{catmore}}" tag in the category.
Arrange for the article to appear at the top of the list of articles in the category, by putting a vertical bar and a space after the category name in the Category: tag (e.g. [[Category:''catname''| ]]).

For such a category/article pair, the guidelines for what other categories the "main article" should be in are still being worked out. Normally articles should not appear both in a category and a "parent" of that category; however an exception should be made for the "main article" of a category — the category system makes more sense if each main article appears in some or all of the categories that the equivalent category appears in. It is optimal for browsing, where the user need not keep bouncing back and forth between the categories of "main" pages and other pages.

If the subject has count, then make the category name plural and create a redirect of that same, plural name, redirecting back to the singular name. For instance City and Category:Cities. That is, create a page called "Cities" and add the line

#REDIRECT [[City]]

This helps to prevent confusion by blocking others from creating a competing page that overlaps in scope and you will be able to use the catmore template without specifying any additional parameters.

In theory, if a main article is categorized correctly in its corresponding category, the use of the catmore template is redundant.

How do I categorize categories which have a main article?

Take John Lennon and Category:John Lennon or The KLF and Category:The KLF. Should all category memberships which relate to Lennon or the KLF (but not to, for example, the state of the article) be added to Category:John Lennon/Category:The KLF and removed from the article? That would seem to follow from literal interpretation of the "no categorizing into a subcategory and category at once" rule, but it forces readers to click an extra time and hides relationships from them.

The article should be left in those categories it would belong to if it had no category of its own; see Wikipedia:Categorization and subcategories#Topic article rule as well as Wikipedia:Categorization#Some general guidelines.

Do categories need parents?

Yes. If you are creating a new category, look for a suitable "parent" category (or several) to assign it to. A good place to look is in articles on related subjects.

If you do not have a parent category, then your category cannot be browsed to via other categories. Also, your category will show up on Special:Uncategorizedcategories.

Can categories be renamed, moved, or redirected?

Yes, "speedy renaming" can be done by listing the category on Wikipedia:Categories for discussion#Speedy renaming. See Wikipedia:Category deletion policy#Speedy renaming procedure.

In particular, redirecting a category does not work well. An alternative is to use the template {{Category redirect}}, which has a bot which helps effect the change. Discuss this with an administrator or at WP:CfD because the bot only works if an admin adds the template to the category.

Also, it is currently impossible to "move" categories like articles are when renamed, keeping their history.

How do I delete a category?

If you feel a category falls within Wikipedia:Category deletion policy, bring it up on Wikipedia:Categories for discussion.

State of the Category feature

The category feature appeared in the MediaWiki software v1.3, which was implemented on Wikipedia in late May 2004.

Initially categories were displayed at the top right of articles, but they were soon moved to the bottom due to layout conflicts. (Not every skin has them at the bottom; eg Cologne Blue has them at top right.)

Known issues

Reported categorisation bugs can be seen at MediaZilla. See also: Wikipedia:Categorization#Known category-related bugs.

Category pages still show old sub-categories and articles after edits [1] [2].

Work-around: You need to make a dummy edit to the category page to fix this, e.g., add a space at the end of a line. Explain this in the edit summary (e.g. "Dummy edit to refresh"), and flag the edit as minor if you have a Wikipedia user account.

Categories can be sub-categories of themselves [3].

Work-around: Don't do it.

Categories cannot be redirected [4].

Work-around: Don't do it, place a link on the page instead if it already exists.

Layout issues:
- Category and interwiki tags produce ugly whitespace [5]
- Category pages show a pre-formatted box from spaces within category lines [6]

Work-around: Edit category pages so that there is only one category tag per line.

How do I report bugs?

Bugs should be reported to the MediaZilla website. (See Wikipedia:Bug reports for instructions.)

How do I request feature enhancements?

Enhancements can be requested at the MediaZilla website. (See also meta:MediaWiki roadmap and Wikipedia:MediaWiki future directions.)

What is the state of categorization?

When trying to categorize an article, it may be difficult to tell into which categories it should be placed. Sometimes when trying to categorize by a field of interest, one intersects with someone else's efforts from another field.

Category policies are still being refined by experimentation, discussion, and polls. Categorizations and systems are likely to be discussed and improved upon for a very long time. To be part of the discussion see Wikipedia talk:Categorization.