Wikipedia:Categorization

[[Category:Wikipedia {{{1}}}s|Categorization]]

This article provides guidelines on creating and organizing categories.

For a quick introduction to categories, see Wikipedia:Category. For everything you ever wanted to know about categories, see Wikipedia:Categorisation FAQ.

When to use categories

Every page in the article namespace should belong to at least one category. Categories should be on major topics that are likely to be useful to someone reading the article.

Article: Michael Jackson

Useful category: Category:Pop singers

Not useful: Category:Musicians whose first name starts with M

Questions to ask to know whether it is appropriate to add an article to a category:

• If the category does not already exist, is it possible to write a few paragraphs or more on the subject of the category, explaining it?
• If you go to the article from the category, will it be obvious why it's there? Is the category subject prominently discussed in the article?

If the answer to either of these questions is no, then the category is probably inappropriate. Note that it is always appropriate to add articles to categories that fit into well established taxonomies. For example, every article about a musical album is categorized in some Category:Artistname albums category, which is in turn categorized in Category:Albums by artist.

An article will often be in several categories. Restraint should be used, however — categories become less effective the more there are on a given article.

There is currently debate about whether an article can be in both a category and its subcategory. In practice, articles are being categorized both ways. For more about this subject see the talk page. Until consensus is reached feel free to do it either way, and please don't start any revert wars about this issue. Here is a summary of some of the views:

1. Articles should not be in both a category and its subcategory, for example Microsoft Office is in Category:Microsoft software, so should not also be in Category:Software.
2. While articles should not usually be in both a category and its subcategory, there are some cases where it make sense, at least temporarily. Some categories represent such inessential aspects of their parent categories, that they are no substitute for inclusion in the parent category. For example, if Pier Paolo Pasolini were in Category:Writers and you were moving him into Category:Murdered writers, you should not remove him from Category:Writers. Yes, that latter category should be refined (for example, to Category:Italian writers), but if you simply "refine" Category:Writers to Category:Murdered writers you make it less likely that Category:Italian writers will be added and you make it less likely that someone who does not already know his biography well will ever find the article.

There is also a related debate concerning the categorisation of articles that have categories of the same name:

1. An article with the same name as a category should be only in that category, for instance, Deism is only in Category:Deism.
2. An article with the same name as a category should be in both that category and the higher level categories. The category will also be in all or some of the higher level categories. Both the article and the category will be listed in the higher level categories. For example, Musical theatre used to be in both Category:Musical theatre and Category:Theatrical genres.
3. An article with the same name as a category should only be in the higher level categories.

Categories appear without annotations, so be careful of NPOV when creating or filling categories. Unless it is self-evident and uncontroversial that something belongs in a category, it should not be put into a category.

Exceptions to the above rules are categories such as Stub categories which are intended to aid the function of Wikipedia editing.

For alternative methods of grouping articles, and the circumstances in which they should be used, see Wikipedia:Categories, lists, and series boxes.

For articles without any stable category, {{catneeded}} tag can be used to bring attention (although Special:Uncategorizedpages exists).

Categories vs. Lists vs. Info boxes

See, Wikipedia:Categories, lists, and series boxes.

Categories applied to articles on people

A separate wikipedia page Wikipedia:Categorization of people was created to help you in designing, applying and checking categories that are used for articles on people.

Categories do not form a tree

Each Wikipedia article can appear in more than one category, and each category can appear in more than one parent category. Multiple categorization schemes co-exist simultaneously. In other words, categories do not form a strict hierarchy or tree structure, but a more general directed acyclic graph (or close to it, see below).

Nevertheless, parts of the category graph will be tree-like, and it may be convenient to think of parts of the category graph as being like multiple overlapping trees.

Cycles should usually be avoided

Although the MediaWiki software does not prevent cycles (loops), these should usually be avoided. Here is an example existing in early November 2005: Category:Academic disciplines - Category:Interdisciplinary fields - Category:Social sciences - Category:Education - Category:Academic disciplines - Category:Interdisciplinary fields ...

Guidelines for assignment of categories

How to create categories

Creating a category is as simple as adding a soft link to the appropriate article in the Category: namespace; for instance, to add Felis silvestris catus to the "fluffy creatures" category, you would edit the article and enter s, and you will find that many articles belong to both lists and categories. You may see some inconsistencies when first creating the category: it may alternate between appearing empty and appearing with your first additions. It will probably correct itself in a few minutes. Note that, although "uncreated" categories ''will'' correctly list articles that have been assigned to them, the category page itself does not exist until it is manually created. The easiest way to create the category page is to follow the edit link from an article and add a parent category and a category description as explained below. ===Creating subcategories=== Create subcategory pages by putting the name of the parent category on a category page that you would like to be the subcategory. Child categories (subcategories) are created by putting <nowiki>, Roses becomes a subcategory of Flowers.

When adding an article to a category, or creating categories, one should be careful to use the correct categories and subcategories. Horizontal categorization, directly below, refers to placing an article in the correct category while vertical categorization refers to placing an article in the correct subcategory.

When assigning an article into categories, try to be thorough in a "horizontal" sense. The topic may be associated with a geographic area, a historical period, an academic subfield, a certain type of thing (like a food or an ornament), and/or a special interest topic (like Roman Empire or LBGT). You might need to poke around the category hierarchy a bit to find the right place. Try searching for articles similar to the article you are categorizing to get ideas or to find the most appropriate place. (For instance, '1990' is more correctly in 'Category:Years' rather than 'Category:Places'.)

In the "vertical" dimension, you should probably be more frugal. A good general rule is that articles should be placed in the most specific categories they reasonably fit in. For example, Queen Elizabeth should not be listed directly under People, but 'Category:Monarchs of the United Kingdom' might be a good place for her. We know that all Queens of the United Kingdom qualify as Famous Britons and as Royalty, and all of those folks qualify as People. But sometimes there's a good reason to assign an article to two categories, one of which is a direct or indirect subcategory of another. For a well-argued case study, see John Lennon.

Whatever categories you add, make sure they do not implicitly violate the neutral point of view policy. If the nature of something is in dispute (like whether or not it's fictional or scientific or whatever), you may want to avoid labelling it or mark the categorization as disputed. Most categorizations are pretty straightforward, though.

Making groups of subcategories

Categories can only list 200 entries at a time. When there are more than 200 entries, only the first 200 will be displayed. To make it easy to navigate, add a TOC (table of contents). TOCs are added by typing:

{{CategoryTOC}} - which adds a complete TOC (Top, 0 - 9, A-Z)

{{CatAZ}} - which adds a TOC without numbers. This is for categories with members that only start with letters.

When a given category gets crowded, also consider making several subcategories. Group similar articles together in a meaningful and useful way that will make it easy for readers to navigate later. Remember that several subcategorization schemes can coexist (for example, if Category:Software gets too big, you don't have to choose between subdividing it by function or subdividing it by platform, you can simultaneously subdivide it in both ways).

A set of related categories often forms a hierarchy or a nexus. This can take several different forms, all of which are welcome and encouraged:

• A taxonomic grouping. For example, Category:South Asian countries is part of a geographical hierarchy. Category:Academic disciplines catalogs divisions between fields of study.

• A functional grouping. Examples: Category:Ancient Rome, Category:World War II, and Category:Commercial item transport and distribution. These bring together articles and subcategories from different fields or taxonomies (history, war, culture, people, companies, industries, technologies) that have an interesting common thread.

• Hybrid forms. For example, Category:Art is both part of the taxonomy of Category:Academia and a cross-reference point for lots of things that have little in common except that they have something to do with art.

• Offshoot forms. For example, Category:Film stubs contains subcategories of Category:Comedy film stubs for comedy films, and Category:Drama film stubs for drama films.

Category membership and creation

When writing the description for a category, give it a parent category. In fact, you should try to give it at least two parent categories. For example, Category:British writers should be in both Category:Writers by nationality and Category:British people. A few categories do only merely subdivide their parent category, but unless the parent category has many potential articles under it, or many potential subdivisions, if you can't think of a second parent category, it might be a better idea to fold your smaller category into the parent.

Wikipedia namespace

Categories relating to the Wikipedia namespace should be added only to the talk page of articles. For example, tags suggesting the article is needs work, would be placed on the talk page as they are relevant to editors, not an aid to browsing in the way ordinary categories are.

User namespace

Categories relating to the User namespace should be added only to Wikipedia-specific categories. Users should not add their user pages to article namespace categories such as Category:People or other subcategories, Category:Biologists etc, which are reserved for pages in the article namespace. However, it is appropriate to add a user page to Wikipedia-specific categories such as Category:Wikipedians or other similar subcategories such as Category:Wikipedian musicians. (See also m:Help:Category for guidelines on category "pollution").

If you copy an article to your user namespace (for example, as a temporary draft or in response to an edit war) you should decategorize it.

Image namespace

See categorizing images.

Category naming

Categories follow the same general naming conventions as articles, for example do not capitalise regular nouns. For specific conventions related to categories, see Wikipedia:Naming conventions (categories).

Categories requirements and usage

User browsing

Categories (along with other features, like cross-references) should help users find the information they are looking for as quickly as possible, even if they don't know that it exists or what it's called.

Links to categories

You can create a link to a category page without adding the page to that category by using a colon before the word Category. Example: [[:Category:Automotive technologies]] appears as Category:Automotive technologies.

Redirected categories

Although it is possible to attempt to redirect categories by adding a line such as #REDIRECT [[:Category:Automotive technologies]] to a category, it is not generally recommended because of limitations in the mediawiki software. Categories "redirected" in this way do not prevent the addition of articles to the redirected category. Articles added to the "redirected" category do not show up as in the target category. Until these issues are addressed (in future versions of the software), #REDIRECT should not be added to category pages.

Category sorting

Contrary to some expectations, text after a pipe ("|") in a category link is not used in place of the category text. Rather, this text is used as the sort key on the category page itself. However, again contrary to expectations, that sort text is not displayed.

For example, the Category:Three-digit Interstate Highways uses this property to sort secondary interstates by their primary. That is, the category link in the article for Interstate 190 (Illinois) is . This causes "Interstate 190 (Illinois)" to be listed right after "Interstate 189" and right before "Interstate 290 (Massachusetts)" under the heading "9" in the category page.

This feature is very useful for categories in which:

• the entries are people, in which case sorting by last name is preferable (example: Category:Presidents of the United States).
• variations in the naming of entries causes inconsistent sorting (example: List of counties in Nebraska, List of counties in Montana, but List of Nevada counties in Category:Lists of U.S. counties).
• the logical sort order is not alphabetical (example: individual month articles in year categories such as Category:2004, using e.g. the sort key "*2004-04" for April).

Using this method to sort category entries is sometimes informally referred to as the pipe trick. However, this use of the pipe character is very different from the original Wikimedia pipe trick which allows one to easily hide parenthetical disambiguation in links.

It is possible to force an article or subcategory to the top of the list by using a non-alphanumeric character as the first after the pipe. For example, using would force that article to be displayed before all the others.

Year categories

In categories which are years, such as Category:2004, special sorting guidelines apply:

• Entries should generally be sorted by topic, so the article 2004 in film, for example, would contain the category reference .
• The article about the year itself, 2004, should be sorted first among all articles by using .
• Articles for individual months, such as October 2004, should be sorted chronologically in the first section on the category page, in this case using .

Interlanguage links to categories

Interlanguage links work just as they do for regular articles; 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 the different languages may have adopted different standards and practices for categorization, so a given category might not exist in other languages. ==Tools== * [[User:Pearle|Pearle]] can be used to automatically move articles from one category to another, get dumps of the category trees, and accomplish some other useful category-related tasks. ==Current projects== See: [[Wikipedia:Categorization projects (current)]] ==Known category-related bugs== Please report new category-related bugs on [http://bugzilla.wikimedia.org/ bugzilla] and list them below. (Bugs higher than 1775 have not been checked) ===Redirects=== * [[bugzilla:100|Redirects do not work properly with Categories]] * [[bugzilla:491|Categories need piping feature to list by alternative name]] (to show redirects next to the articles they redirect to in categories, when appropriate) * [[bugzilla:710|Redirect to category page doesn't work]] * [[bugzilla:927|Problem categorizing redirects]] * [[bugzilla:1333|Would like the ability to list an article under multiple names in its categories]] * [[bugzilla:1476|Category tag on redirect pages does not work]] ===Special:Categories=== * [[bugzilla:146|Special:Categories:Add the number of articles in the category]] * [[bugzilla:461|Link to Special:Categories should be customisable]] * [[bugzilla:844|Special:Categories should be paged by letter, like Special:Allpages]] * [[bugzilla:1064|Special:Categories don't display categories with no article]] ===Large categories=== * [[bugzilla:1058|dealing with large categories]] * [[bugzilla:1212|On paged categories, article totals and subcat totals are incorrect]] * [[bugzilla:1211|Subcategory paging is not separate from article paging]] * [[bugzilla:1502|Table of contents for Categories]] ===Updating problems=== * [[bugzilla:632|Slow deletion of members from categories]] * [[bugzilla:939|changes to links in a template do not update 'links', 'categorylinks', etc for pages including it]] ===General=== * [[bugzilla:73|Images inappropriately added to categories]] * [[bugzilla:87|Category and interwiki tags produce ugly whitespace]] * [[bugzilla:243|Add anchor tags to the headers used on category pages]] * [[bugzilla:144|Special:Recentchangeslinked for particular categories]] * [[bugzilla:337|Characters in category names]] * [[bugzilla:449|uncategorized pages report speedup hack]] * [[bugzilla:450|Categories need to be structured by namespace]] * [[bugzilla:489|Categories link at bottom of article points to wrong place]] * [[bugzilla:510|Feature request: Special random category page]] * [[bugzilla:516|Ability to filter user contributions by time (e.g. "January 2003") or category]] * [[bugzilla:626|Different new page text for each namespace (enhancement)]] (the text you get for completely and partly empty category pages, category talk pages, etc.) * [[bugzilla:633|Pluralization in listing totals]] * [[bugzilla:706|syntax such that a (template) page can be un-categorized, but still categorise pages transcluding it]] * [[bugzilla:827|feature request: "newest changes" display for categories, "start from" ... input mask]] * [[bugzilla:835|syntax to transclude a page without the containing page inheriting categories, interlanguage links]] * [[bugzilla:900|Category page listings have unbalanced columns]] * [[bugzilla:931|automatic edit summary for categorizing pages]] * [[bugzilla:943|RSS feed for category updates]] * [[bugzilla:1029|Whitelist doesn't work correctly for categories]] * [[bugzilla:1106|Feature request: boolean search in categories]] * [[bugzilla:1119|Page move updates categories with sorting tweak]] * [[bugzilla:1169|Unstable categories (non-ASCII characters)]] * [[bugzilla:1239|New page created, db lag, result in double entries in categories]] * [[bugzilla:1242|Category list missing on edit page]] * [[bugzilla:1289|Feature request: Category reverse sort by date]] * [[bugzilla:1467|Subpages don't work in Help_talk: and Category_talk:]] * [[bugzilla:1701|Korean wikipedia's categories need new sectioning scheme]] * [[bugzilla:1710|Ability to watch all articles in a category]] * [[bugzilla:1745|can't edit the history versions of the categories!]] * [[bugzilla:1775|Request: parameters in categories]] ==See also== *[[Wikipedia:Browse]] - A navigation page that includes links to high-level categories *[[m:Help:Category]] *[[Wikipedia:Category]] *[[Wikipedia:Categorisation FAQ]] *[[m:Categorization requirements]] (original guidelines for category proposals and implementations) *[[:Category:Knowledge representation]] - Material related to concept categorization. *[[Wikipedia:Categories for deletion]] ===Browsing categories=== *[[:Category:Orphaned categories]] - Category for categories that need reparenting. *[[Special:Categories]] - Lists all existing categories alphabetically. *[[:Category:Categories]] - List of top-level categories. Requires this category be defined on the top of a tree. *[[:Category:Fundamental]] - Fundamental knowledge categories. [[Category:parent_category_name]] on the lower-level category pages. For example, on a (sub)category page called category:Roses you put [[Category:Flowers]] [[Category:2004|*]] [[Category:2004|*2004-10]] [[Category:2004|Film]] while 2004 Canadian budget would contain the reference [[Category:2004|Canadian budget]]; List of religious leaders in 2004 would contain [[Category:2004|Religious leaders]] [[Category:Fluffy creatures]] at the bottom, but before interlanguage links. Although the link will not appear in the article text, a page called Category:Fluffy creatures will automatically list alphabetically all articles that contain the [[Category:Fluffy creatures]] link. The appeal of categories is that unlike lists, they update themselves automatically, and that one can use them to quickly find related articles. However, categories are not a substitute for list</nowiki> (note the space) or [[Category:Ford|*Ford Motor Company]] [[Category:Three-digit Interstate Highways|90-1 Illinois]] [[Category:Wikipedia categorization|*]] [[Category:Wikipedia how-to|{{PAGENAME}}]] [[Category:Wikipedia style guidelines|{{PAGENAME}}]] [[be:Вікіпэдыя:Гіерархія]] [[ca:Viquipèdia:Categorització]] [[da:Wikipedia:Kategorisering]] [[de:Kategorie:Mathematik]] in Category:Mathematics