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Categorization is a feature of Wikipedia's software, enabling pages to be placed in categories which can then be used by readers to find sets of articles on related topics. Categories can be defined as subcategories of other categories, and classes of categories can be formed. These allowing easy navigation between connected subject areas. This helps readers find articles on particular topics even if they don't know which articles exist or what they are called.

The tree-like structure navigated is imagined to root at the top, and branch downward into subcategories which inherit the expanding set of articles and set of categories of all their ancestors, the most immediate of which is called the parent category. The terms subcategory and parent category refer to the navigational or structural aspects of the category system, while the term category can refer to either its navigational aspect or its substantial aspect—the actual content of interest that structure supports.

Adding content or structure, deciding the members of a category, is simply creating a set. When we learn the nature of a particular set, we add members correctly. When we learn the nature of each type of category, we can then categorize member pages correctly. We will learn what types of categories there are, what issues have arisen in the system, and how to alleviate those issues by adding member pages after first gaining an understanding of how the system best functions.

Parent categories are in the categories box and subcategories are in the top section of a category. The content of a category, the members, are in the Pages and Media sections. The mechanics of a category page are described in, while the nature of a category page is described here.

Quick summary

 The hierarchy of categories is a tree-like structure, rooted at the top, and growing downward, as subcategories evolve to inherit the set of members aggregated down to that point. 

In Wikipedia's Category namespace the term category means a category page. A category has two main purposes. (1) It structures its own namespace, Category, by listing subcategories in a Subcategories section, and listing parent categories in a categories box. (2) It structures the content of all other namespaces by listing closely related article titles in a Pages or Media section. A member of a category can belong to either purpose. The second purpose, the content categories, are divided conceptually into project, stub, and maintenance categories.

Categories with no members in the Pages section serve a purely structural function (for the Category namespace). The term member, is used as in "member of a set". Each category page represents two sets on it's page, one for structure, one for content. Each category page presents only its own subset. It is important to keep in mind, when categorizing, that each category represents the entire set of members of all the categories above it. Each category represents its ancestor categories, while also presenting its own subset of members, listed on its page, and adding to the larger set it actually represents down to that point. The context will determine whether the term member means a link to an article or a link to a category. The term category, then, can refer directly to a subset or indirectly to the entire set down to that point, and it can refer to either of the two types of sets, the categorical set, or the content set.

When the name of a member of the structural set is the same as the name of a member of its content set a certain kind of categorization issue arises named after the concept of "eponomy". Other common issues unique to categorization are duplication, circularly referencing branches, and over-categorization (compare with Notability for articles).

Category pages have a lead section with a layout not dissimilar to the lead section of a main article, but the lead section of a category page can also contain classifications. Articles and categories both grow and may spin-off parts to create another page; these create subcategories and distinguished subcategories.

The category system

 Considering subcategories only, Wikipedia's category system forms a hierarchical structure of multiple, interconnected tree structures. Each category has a direct path branching to the root category, Contents, but because subcategories can have more than one immediate parent, the system as a whole will approximate a directed acyclic graph. 

Considering only a category and, for now, only the articles in that category, there are two basic types of relations between the category's title and the articles it holds. A topic category will have a title that names a topic about some subject matter, and each member page will be an article about that subject. The more articles that display on a topic category page, the broader the subject is, and the more subtopics that are required (to keep any one article from growing too large). A list category on the other hand, has a name more likely to denote a pluralty, and each member page will be a notable instances of that subject in its entirety. There can become endless numbers of such articles describing notable instances in some subject area, whereas for topic categories the notable, factual knowledge in a subject area is relatively limited. Now for that same category page, the subcategories will have the same considerations: some subcategories will be topical in nature, and some will have the nature of lists. The nature of such subcategories is discerned by what kind of articles they hold. A list-and-topic category will have characteristics of both.

For example, Music is a topic category, and Musicians is a list category. An example of a list-and-topic category is Voivodeships of Poland. It contains an article about a particular voivodeship, but it also contains an article about voivodeship.

If the member articles of one category page belong logically to to a second, the first is made a subcategory of the second. A category page is subcategorized when a category declaration is placed in it. The category Humans belongs to the category Primates. For the Human category to appear in the Primate category, the Category:Humans page makes the category declaration

If B is a subcategory of A, then A is said to be a parent category of B. The branch Humans-Primates-Mammals-Vertebrates contains four categories. If the category declaration in a category page is an arrow from itself (the subcategorized category) to the "parent" category, and if the root category is at the bottom, all the arrows point downward. (See the figure and its caption.) The direction of a category branch (a sequence of logical categorizations of pages) is counter-intuitive. Of the four category pages in the branch given, the first three contain the category declarations that make them subcategories, and the fourth category page does not contain a category declaration that points toward the other three. Vertebrates is a parent category of this branch.

Categorizing pages

Every Wikipedia article should belong to at least one category. Similarly every category should be placed in at least one parent category. But before this endeavor is even started for your category of interest, there are some important considerations to make. 
  • Although it is clear that a list category page might be subcategorized under that subject, it would incorrect to do it vice versa (to subcategorize a topic category under a list category).
  • Certain issues arise when an an article title has the same name as its category title, so this situation has a name. It is termed an eponymous category. These issues are covered in Eponymous categories (below).
  • Articles should be placed in the lowest level category possible. They do not need a category declaration toward every category that would logically contain it. A single, well targeted category declaration will place that article in a category which will itself be properly contained (subcategorized).
  • Issues could arise when placing at article in more than one related category, and these are covered in Duplicate categorization rule (below).
  • Disambiguation pages belong to special categories (see Disambiguation); most redirects are not categorized, though there are exceptions (see Categorizing redirects). For the categorization of pages in other namespaces, and categories used for project management purposes, see Project categories below.
  • An article should be placed in all the existing categories to which it logically belongs, subject to the duplicate categorization rule stated below. It should be clear from the verifiable information in the article why it was placed in each of its categories. Use the {{Category unsourced}} template if you find an article in a category that is not shown by sources to be appropriate, or the {{Category relevant?}} template if the article gives no clear indication for inclusion in a category.
  • Normally a new article will fit into existing categories – compare articles on similar topics to find what those categories are. If you think a new category needs to be created, see the section What categories should be created below. If you don't know where to put an article, add the {{uncategorized}} template to it – other editors (such as those monitoring Wikipedia:WikiProject Categories/uncategorized) will find good categories for it.
  • Categorize articles by characteristics of the topic, not characteristics of the article. A biographical article about a specific person, for example, does not belong in Category:Biography. (For exceptions, see Project categories below.)
  • An article should never be left with a non-existent (redlinked) category on it. Either the category should be created (most easily by clicking on the red link), or else the link should be removed or changed to a category that does exist.
  • Articles on fictional subjects should never be categorized in a manner that confuses them with real subjects. A "list" category containing members of a series, such as Category:European countries or Category:Presidents of the United States, should only contain real examples of those series. If a list category for fictional subjects has a real-life counterpart, as with Category:Fictional Presidents of the United States, its contents should be expressly identified as fictional in the name of the category itself. This is not necessary where the grouping is purely fictional, as with Category:Klingons. Fictional subjects may only be mixed with real ones only in topical categories, i.e., ones that do not classify a series of real things or people. In such topical categories, there is not the risk of confusing fiction with fact as with list categories.

The order in which categories are placed on a page is not governed by any single rule (for example, it does not need to be alphabetical, although partially alphabetical ordering can sometimes be helpful). Normally the most essential, significant categories appear first. If an article has an eponymous category (see below), then that category should be listed first of all. For example, Category:George Orwell is listed before other categories on the George Orwell page.

Eponymous categories

Often an article and a topic category will share the same name, as in George W. Bush and Category:George W. Bush, or occasionally similar names referring to the same thing, as with Mekong and Category:Mekong River. Such a category is called an eponymous category. Naturally the article itself will be a member of the category (and should be sorted to appear at the start of the listing, as described below under Sort order). 

The question arises as to whether eponymous categories should be placed in (made subcategories of) the categories which their corresponding articles belong to. Logically they usually should not (for example, France belongs to Category:European countries, but Category:France does not constitute a subset of European countries). However, by convention, many categories do contain their articles' eponymous categories as subcategories. In any case, an article should not be excluded from any list category on the grounds that its eponymous category is made a "subcategory" of that category. For the purposes of the duplicate categorization rule stated above, such eponymous categories are considered distinguished subcategories (in fact they are not true subcategories at all).

In other cases, eponymous categories have been categorized separately from their articles. In this case it will be helpful to readers if there are links between the category page containing the articles and the category page containing the eponymous categories. An example of this setup is the linked categories Category:American politicians and Category:Categories named after American politicians, using the template {{CatRel}}.

A clear link to the main topic article from an eponymous category page can be created using the template {{catmore}}.

What categories should be created

Categories should be useful for readers to find and navigate sets of related articles. They should be the categories under which readers would most likely look if they were not sure of where to find an article on a given subject. They should be based on essential, "defining" features of article subjects, such as nationality or notable profession (in the case of people), type of location or region (in the case of places), etc. Do not create categories based on incidental or subjective features. Examples of types of categories which should not be created can be found at Wikipedia:Overcategorization. Discussion about whether particular categories should exist takes place at Wikipedia:Categories for discussion. 

It should be remembered that categories are not the only means of enabling users to browse sets of related articles. Other tools which may be used instead of or alongside categories in particular instances include lists and navigation boxes. For a comparison of the uses of these techniques, see Categories, lists and navigation templates.

Categorizations appear on pages without annotations or referencing to justify or explain their addition; editors should be conscious of the need to maintain a neutral point of view when creating categories or adding them to articles. Categorizations should generally be uncontroversial; if the category's topic is likely to spark controversy then a list article (which can be annotated and referenced) is likely to be more appropriate.

Before creating a new category, check whether a similar category already exists under a different name (for example, by looking on the likely member pages or in likely parent categories).

Categories follow the same general naming conventions as articles; for example, common nouns are not capitalized. For specific rules, see Wikipedia:Naming conventions (categories).

For proposals to delete or rename categories, follow the instructions at Categories for discussion.


Shortcut: WP:SUBCAT

Although there is no limit on the size of categories, a large category will often be broken down 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 broken down using several coexisting schemes; for example, Category:Albums is broken down by artist, by date, by genre etc. Intermediate categories 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 in the intermediate category Category:Albums by artist.

Not all subcategories serve this systematic "breaking down" function; some are simply subsets which have some 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 distinguished subcategories.

The identification of distinguished and non-distinguished subcategories is important for the application of the duplicate categorization rule. It is useful to state in category descriptions whether or not a given category is a distinguished subcategory of a parent category. Use the {{allincluded}} and {{distinguished subcategory}} templates to specify the particulars. If no such information is present, determine the status of a subcategory by common sense and observation of the way existing articles are categorized.

Categories which are intended to be fully broken down into subcategories can be marked with the {{catdiffuse}} template. This 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 broken down into subcategories, you can add the {{verylarge}} template to the category page.

Subcategories defined by ethnicity and sexuality are often classed as distinguished. For example, Category:African American baseball players is a distinguished subcategory of Category:American baseball players, as this category is not broken down systematically by ethnicity. See also Wikipedia:Categorization/Gender, race and sexuality.

Remember that subcategories will often belong in at least two parent categories. For example, Category:British writers should be in both Category:Writers by nationality and Category:British people. When making one category a subcategory of another, ensure that the members of the first really can be expected (with possibly a few exceptions) to belong to the second also. If two categories are closely related but are not in a subset relation, then a link to one can be included in the other's category description (see below).

Duplicate categorization rule

Shortcut: WP:DUPCAT

If a page is contained logically in both a category and a subcategory of that category, it must be considered whether it should still be placed directly into the first (parent) category. The rule normally applied is as follows, based on the definition of distinguished category as given above:

  • If category B is a non-distinguished subcategory of category A, then pages belonging to category B (directly or through further subcategories) are not placed directly into category A. (See also Eponymous categories below.)
  • If category B is a distinguished subcategory of category A, then pages belonging to category B are placed directly into category A if otherwise appropriate.

For example, Angers Bridge is not placed directly into Category:Bridges, because it belongs to the non-distinguished (systematic) subcategory Category:Bridges in France. On the other hand, pages are not excluded from Category:Bridges in New York City on the grounds that they also belong to Category:Toll bridges in New York City, since the latter is a distinguished subcategory.

Display of category pages

Form of entries

The entries as displayed on category pages are the exact names of the pages that have been placed in the category (minus the Category: prefix in the case of subcategories). It is not possible to change the way the entries are displayed using piping or any similar technique. 

If the desired display text in a particular category is different from the title of the article, it may be appropriate to categorize a redirect as well as the article itself. For example, if John Smith was notable as both a musician and a writer, but used the stage name Johnny Rocket in his musical career, then the musician category declarations can be placed on the "Johnny Rocket" redirect page as well as on "John Smith". (Redirects appear in italics in category listings.) See also Wikipedia:Categorizing redirects.

Sort order

Shortcut: WP:SORT

It is possible to change the order of entries listed on a category page. This order is based on the sort key associated with each entry (notice that sort keys themselves are not displayed). If no sort key is defined explicitly for an entry, the sort key used is the page name as displayed.

Entries are intended to be arranged alphabetically, and the lists are broken down by initial character. However the "alphabet" used here is based on the Unicode character listing, and may give unexpected results. For example, all capital letters come before all lower case letters; modified letters come after all unmodified letters; and spaces come before anything else.

Using sort keys

To change the position of an entry in the list, define an explicit sort key for that entry. This is done in the original category declaration on that entry's page, by adding the desired sort key after a pipe. For example,  places the current page in the "Music" category with the sort key "Trombone". 

If a page is to be given the same sort key in all or several of its categories, the magic word can be used. The effect of the magic word does not depend on its position in the text, but it is conventional to place it just before the list of category declarations. For instance, on George Washington, type to define "Washington, George" as the page's sort key for all categories, except any for which a different sort key is defined explicitly.

Default sort keys are often defined even where they do not seem necessary – when they are the same as the page name, for example – in order to prevent other editors or automated tools from trying to infer a different default. Where a default sort key needs to be overridden with the name of the page, Religionwiki:Categorization can be used as the sort key (this means that it will still work if the page is moved).

Sort keys are case sensitive, so care must be taken in specifying capitalisation. For example, do not begin a sort key with a lower case letter unless you want the article to appear on the category page separate from articles sorted with an upper case letter, under a lower case letter heading. A case-insensitive sort can be achieved by following the convention that initial letters of words are capitalized in the sort key, but other letters are lower case. For example, use "Dubois" in sort keys rather than "DuBois".

Typical sort keys

  • Categories of people are usually sorted by last name rather than first name, so "surname, forename" sort keys are used as in the George Washington example above. For more information, see Wikipedia:Categorization of people#Ordering names in a category.
  • Entries containing modified letters should be sorted as if the letters were unmodified (for example, "Lodz" should be used as the sort key for Łódź).
  • Entries containing numbers sometimes need special sort keys to ensure numerical rather than alphabetical ordering (for example, 19 and 103 come before 2 in alphabetical order, and IX comes before V). So Haydn's 13th symphony might have the sort key "Symphony 013", the zero ensuring that it is listed before symphonies 100–108; Pope John IX might have a sort key "John 09". It is important to stick to the same system for all similar entries in a given category.
  • Similar systematic sort keys are used in other categories where the logical sort order is not alphabetical (for example, individual month articles in year categories such as Category:2004 use sort keys like "*2004-04" for April). Again, such systems must be used consistently within a category.
  • In some categories, sort keys are used to exclude prefixes that are common to all or many of the entries, or are considered unimportant (such as "List of" or "The"). For example, in Category:2004 the page 2004 in film would have the sort key "Film", and in Category:2004 in Canada the page 2004 Canadian federal budget would have the sort key "Federal Budget".
  • Use a space (" ") as the sort key for an article matching an Eponymous category, or a key article for the category. This ensures these appear at the start of the listing for that category, as in .
  • Use an asterisk ("*") for any "List of ..." and other pages that should appear after the key article and before the main alphabetical listings.
  • Similarly, in certain exceptional circumstances, subcategories may be grouped together at the beginning of a category listing by means of these special character sort keys. For example, in Category:Australia stubs general topics are grouped together by using a leading space as a sort key, and regional stubs are grouped together using a leading asterisk.
  • To place entries after the main alphabetical list, use sort keys beginning with tilde ("~"). Other characters used for this purpose are "µ", commonly used to place stub categories at the end of subcategory lists; "β" for book subcategories; and "τ" for categorizing templates.

Split display

When there are more than 200 entries in a category, only 200 are displayed on the screen at a time. Users can navigate between screens using the "previous 200" and "next 200" links provided. The text of the category page itself appears at the top of every screen. The URL for a category subpage with up to 200 entries listed alphabetically from a given point takes the following form: 

(this example produces a page listing all the entries in Category:Living people alphabetically starting from "Aq").

To make navigating large categories easier, add a table of contents to the category page. This can be done using the following templates:

  • {{CategoryTOC}} – adds a complete table of contents (Top, 0–9, A–Z)
  • {{CatAZ}} – the same as {{CategoryTOC}}, but without the numbers 0–9
  • {{LargeCategoryTOC2}} – adds a complete table of contents with five subdivisions for each letter (Aa Ae Aj Ao At)
  • {{LargeCategoryTOC}} – adds a complete table of contents with twenty-six subdivisions for each letter (Aa ... Az)

Subcategories are split alphabetically along with the articles, which means that the initial screen of a split category may not include all its subcategories. To make all subcategories display on each screen, add a category tree to the text of the category page, as described below under Displaying category contents on pages.

Category description

Rather than leave the text of a category page empty (containing only parent category declarations), it is helpful – to both readers and editors – to include a description of the category, indicating what pages it contains, how they should be subcategorized, and so on. The description can also contain links to other pages, in particular to other related categories which do not appear directly as subcategories or parent categories, and to "sister categories" on other projects, such as Commons. 

Various templates have been developed to make it easier to produce category descriptions, such as {{catmore}}, {{cat see also}}, {{CatRel}}, and {{cat see also commons}}. For more of these, see Category namespace templates. Another technique that can be used is described at Wikipedia:Classification.

Project categories

The categories that readers are intended to see on article pages and use for browsing are called content categories. These are part of the encyclopedia and should be maintained as such, generally being kept separate from non-article pages and other categories which are addressed to editors rather than readers. Content categories are based on features of the subject matter of articles, not on an article's current state or other classifications specific to the Wikipedia project. 

Categories which are not intended to serve as content categories are called project categories. There are various types of these, including stub categories (generally produced by stub templates), maintenance categories (often produced by tag templates such as {{cleanup}} and {{fact}}, and used for maintenance projects), WikiProject and assessment categories, and categories of pages in other namespaces. These categories are used by Wikipedia editors or automated tools, and do not aid readers' browsing.

Article pages should be kept out of project categories if possible. For example, the templates that generate WikiProject and assessment categories should be placed on talk pages, not on the articles themselves. If it is unavoidable that a project category appears on article pages (usually because it is generated by a maintenance tag that is placed on articles), then in most cases it should be made a hidden category, as described under Hiding categories below.

User pages

Shortcut: WP:BADCATS

User pages are not articles, and thus do not belong in content categories such as Category:Living people or Category:Biologists. They can however be placed in user categories – subcategories of Category:Wikipedians, such as Category:Wikipedian biologists – which assist collaboration between users. See Wikipedia:User categories for further information.

Similarly, user subpages that are draft versions of articles should be kept out of content categories. If you copy an article from mainspace to userspace and it already contains categories, remove them or comment them out. Restore the categories when you move the draft back into article space.


Images are typically put in categories that contain only images. See Categorizing images for more information. To find image categories, navigate from Category:Wikipedia images by subject or its parent category Category:Wikipedia images. 

Hiding categories

In cases where, for technical reasons, project categories appear directly on articles rather than talk pages, they should be made into hidden categories, so that they are not displayed to readers. This rule does not apply to stub categories or "uncategorized article" categories – these types are not hidden. 

To hide a category, add the template {{hiddencat}} to the category page (the template uses the magic word ). This also places the page in Category:Hidden categories.

A logged-in user may elect to view all hidden categories, by checking "Show Hidden Categories" on the "Misc" tab of My Preferences. Notice that "hidden" parent categories are never in fact hidden on category pages (although they are listed separately).

Categorization using templates

 Many templates include category declarations in their transcludable text, for the purpose of placing the pages containing those templates into specific categories. This technique is very commonly used for populating certain kinds of project categories, including stub categories and maintenance categories. 

It is not recommended that articles be placed in ordinary content categories in this way.

  • It becomes difficult to tell looking at the page source if a page is in a category or not.
  • Removing a special page from a category becomes difficult, often requiring templating skills and calling for an admin to make the change to a protected template.
  • The technique is likely to lead to pages being miscategorized, or their categories being listed in an undesired (certainly less controllable) order. In some instances, it may even have the unintended result of creating inappropriate categories, such as Category:Cities and towns in. Further, if such a template is used on the category page for the transcluded category, a confusing loop is generated, with the category listed as a subcategory of itself.
  • Some users keep sandbox pages with templates on them, or even add templates directly to their user pages, which thus also end up inappropriately filed in articlespace.
  • The search term "incategory" will not pick up these pages.
  • Pages categorised this way are harder to deal with for automated processes. In particular those that read the wiki-text (either from the site or from database dumps) will not be able to find the categories without intimate knowledge of every category transcluding template, those that use "incategory" will also get wrong results.
  • Changes to category structures, moving, renaming, merging and splitting also become harder.

Notice that changing the category in a template does not cause all pages with the template to be recategorized immediately – pages may need to be edited before their categorization changes. This means that category lists for categories populated in this way may not always be up to date.

Category declarations in templates often use Religionwiki:Categorization as the sort key, particularly if they are designed to be placed on talk pages, as this suppresses the prefix Talk: from the sort keys. This also suppresses any DEFAULTSORT defined on the page.

Redirected categories

Although it is possible to attempt to redirect categories by adding a line such as  to a category, it is not generally recommended because of limitations in the mediawiki software. Until these issues are addressed (in future versions of the software), #REDIRECT should not be added to category pages. 

"Soft" redirects for categories can be created using {{Category redirect}}. A Bot traverses categories redirected in this manner moving articles out of the redirected category into the target category; see Template talk:Category redirect.

Interlanguage links to categories

Interlanguage links work just as they do for regular articles:  in Category:Mathematics connects to the German counterpart. This can be a useful way to compare coverage, or to look for articles in need of interlanguage links. Note that different Wikipedias may have adopted different standards and practices for categorization, so not all categories have equivalents in other languages. 


Displaying category contents on pages

To display the subcategory tree and (optionally) member pages of a given category on any page, use the CategoryTree extension (see the documentation page for full details). The basic syntax is 
  • <categorytree>Category name</categorytree>

to display just the subcategory tree, and

  • <categorytree mode=pages>Category name</categorytree>

to display member pages as well.

Retrieving category information

Raw information about the members of a category, their sortkeys and timestamps (time when last added to the category) can be obtained from the API, using a query of the form: 

Linking to categories

Outside mainspace, the following templates can be used to display a category in different ways, or link to its maintenance pages. 
  1. produces
  2. produces
  3. produces

Searching for articles in categories

In addition to browsing through hierarchies of categories, it is possible to use the search tool to find specific articles in specific categories. To search for articles in a specific category, type incategory:"CategoryName" in the search box. This can be used to find articles that are members of more than one category (see Wikipedia:Category intersection for a proposal for a more sophisticated version of this feature). For example, enter the search text 
incategory:"Suspension bridges" incategory:"Bridges in New York City"

to find the articles that are common to both categories—the suspension bridges in New York City—as here.

Similarly, an "OR" can be added to join the contents of one category with the contents of another. For example, enter

incategory:"Suspension bridges" OR incategory:"Bridges in New York City"

to return all pages that belong to either (or both) of the categories, as here.

Note that using search to find categories will not find articles which have been categorized using templates.

See also

For browsing

For maintenance