Help:Categorization

This article provides guidelines on creating and organizing categories.

When to use categories

Categories (along with other features like cross-references, lists, and infoboxes) help users find information, even if they don't know that it exists or what it's called.

Every page in the article namespace should belong to at least one category. Categories should be 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 determine 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 the article was put in the category? 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.

Guidelines

Some general guidelines

1. Categories are mainly used to browse through similar articles. Make decisions about the structure of categories and subcategories that make it easy for users to browse through similar articles.
2. An article will often be in several categories. Restraint should be used as categories become less effective the more there are on any given article.
3. Articles should not usually be in both a category and its subcategory. For example Golden Gate Bridge is in Category:Suspension bridges, so it should not also be in Category:Bridges. However there are occasions when this guideline can and should be ignored. For example, Robert Duvall is in Category:Film actors as well as its subcategory Category:Best Actor Academy Award winners. See #5 for another exception. For more about this see Wikipedia:Categorization/Categories and subcategories
4. Check to see where siblings of the article reside. If there are few if any articles in a category, the article probably belongs in one of the subcategories.
5. Articles should be placed in categories with the same name. However, the article and the category do not have to be categorized the same way. The article can also be placed in categories populated with similar articles. The category can be put into categories populated with similar subcategories. For an example of this see George W. Bush and Category:George W. Bush.
6. There are often occasions when articles might ideally be moved from a category to two or more of its subcategories, but not all of the subcategories exist. In such cases consider creating the additional subcategories, but if you decide not to do so, leave the articles in the parent category for the time being.
7. Bend the rules above when it makes sense, but only if no other solution can be found.
8. 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. A list might be a better option.
9. If you don't know where to put an article don't worry about it. Instead of adding a category, use the {{uncategorized}} tag to bring attention to the article. Editors who love to categorize articles will find a good home for your article.

Categories vs. Lists vs. Info boxes

For alternative methods of grouping articles, and the circumstances in which they should be used, 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. When applying the guidelines above, consider each tree to be independent of the overlapping trees. A person browsing through a hierarchy should find every article that belongs in that hierarchy. This can lead to a good deal of debate as to what the hierarchies actually are. To clarify the structure of the hierarchy and help people browse through it, you can add a classification to each category. For more about this, see Wikipedia:Classification.

Cycles should usually be avoided

Although the MediaWiki software does not prevent cycles (loops), these usually should be avoided. Cycles can be confusing to some readers, they can challenge some automated searching processes and they can grow quite large. For example, in January 2006 a 22-member category cycle was discovered and eliminated.

However, acceptable loops also exist. Self-referencing systems such as the meta- fields naturally create cycles that provide many examples. This type of cycle involves making a category one of its own subcategories. A real-world example of a self-referencing system is “education about education,” such as:

Classification: Education: Social sciences: Academic disciplines: Academia: Education: ...

Another type of cycle involves making two categories subcategories of each other. Loops such as these can be avoided by linking the categories manually to each other by adding "See also:Category:Foo" to each category page. For an example of this see Category:World Trade Center and Category:September 11, 2001 attacks.

How to put an article into categories

Template:Style Adding an article to a category is as simple as editing the article and adding a link to the category. For instance, to add Felis silvestris catus article to the "fluffy creatures" category, you would edit the article and enter [[Category:Fluffy creatures]] at the bottom, but before interlanguage links. The appeal of categories is that unlike lists, they update themselves automatically, and you don't have to edit the category to add an article to it. However, categories are not a substitute for lists, and you will find that many articles belong to both lists and categories.

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 LGBT). 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.

In the "vertical" dimension, Wikipedia has traditionally been more frugal, placing articles only in the most specific categories they reasonably fit in. Thus, if there is a Category:American film actors, John Wayne would go there and not in Category:Film actors or Category:American actors. However, there is a school of thought that argues that, because different users may be interested in different categories, and because placing articles in multiple categories takes up minimal additional space, in some cases one should place articles in all the categories that apply.

For more about this see Wikipedia:Categorization/Categories and subcategories

How to create categories

Creating a category is as simple as adding a link to a category that doesn't yet exist. For instance, to create the "fluffy creatures" category, you would edit an article and enter [[Category:Fluffy creatures]] the same way as adding it to any other category. The Category:Fluffy creatures will automatically be created when the edit is saved.

Category naming

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

Look before you leap

Before creating a category, look to see if one already exists. The best way to do this is to first add the category to your article but preview before saving. If the category appears in blue at the bottom of the page, the category already exists. If it is in red, then you will be creating a new category. Check the capitalization of the category name. For any red categories, you should look for categories with similar names before creating a new category. One way to do this is to think of the parent category for the new category. Search for it and then look at the subcategories in the parent. You may find that a category already exists that is similar to the one you are thinking about creating.

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 red category link from your article and create a new category page with a parent category and a category description as explained in the next section.

How to create 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 [[Category:parent_category_name]] on the lower-level category pages. For example, on a (sub)category page called category:Roses you put [[Category:Flowers]], Roses becomes a subcategory of Flowers.

When writing the description for a category 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.

How to delete a category

Please refer to Wikipedia:Categories for discussion

How to rename a category

Please refer to Wikipedia:Categories for discussion

Organizing categories

Large categories

When there are more than 200 entries in a category, only 200 are displayed on the screen and users have to click through multiple screens to see all the entries. 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).

Grouping categories

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.

Other requirements

Wikipedia namespace

Categories relating to the Wikipedia namespace should be added only to the talk page of articles. For example, tags suggesting the article needs work would be placed on the talk page as they are relevant to editors and 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 in one of the following ways, (where foobar is the category name):

1. [[:Category:foobar]], note the extra : before Category.
2. {{cl|foobar}}, see {{cl}}
3. {{ccl|foobar}}, see {{ccl}}
4. {{lcs|foobar}}, see {{lcs}}

Image namespace

See categorizing images.

Keep cats out of the sandbox

Categories should not be put on articles that you are working on in the sandbox, nor on any page that you are using as a sandbox (such as an article draft that you are writing in a subpage of your userspace). In such cases you can add <nowiki> before the categories and </nowiki> following them, so that they will display without creating category listings. When the draft becomes an actual article you can remove the markup.

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.

"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.

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. One common application is to ignore "The" in article names, so [[Category:Rock and Roll Hall of Fame inductees|Beatles, The]] will make "The Beatles" list under B rather than T in the category.

As another 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 [[Category:Three-digit Interstate Highways|90-1 Illinois]]. 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 [[Category:Ford| Ford Motor Company]] (note the space) or [[Category:Ford|*Ford Motor Company]] would force that article to be displayed before all the others. Many editors feel that the space character produces the best aesthetic appearance when the category is displayed. Using a space or asterisk after the pipe is the customary way to categorize an article in a category with the same name, indicating that the article is the main topic article for that specific category. For an example, see Category:Suspension bridges. Using {{Catmore}} may be preferable - no consensus has been established yet. To list at the end (after z) of a category, the sort key ~ can be used [[Category:Polyhedra|~Polyhedra templates]].

Other specifics:

• For more detailed guidelines about sorting names of people, see Wikipedia:Categorization of people#Ordering names in a category.
• Don't start the category sort key with a lower case letter, unless you want to create a separate caption with that lower case letter in the category (note that the first lower case letter caption starts only after the last upper case letter caption)
• When trying to sort with numbers (e.g. wikipedia:Naming conventions (pieces of music)), don't forget to add an extra zero when more than 9 entries in the category are expected; and a second extra zero when more than 99, etc...: [[Category:Symphonies by Joseph Haydn|Symphony 13]] → [[Category:Symphonies by Joseph Haydn|Symphony 013]] (he wrote 108 symphonies). Categories sort by the first character, so leaving out the preceding zero would cause 10 to be sorted before 2.
• Ordinals often have to be converted to Arabic numerals: e.g. Pope John IX: [[Category:Popes|John 09]] (+ zero added, there are XXIII popes with the name John)
• Don't forget to convert letters with diacritics, or non-standard letters to the nearest standard letters (that is: "standard" in English, at the time Wikipedia is written), examples:
  • Diacritics are omitted: e.g. Étretat: [[Category:Communes of Seine-Maritime|Etretat]], or: Ål: [[Category:Municipalities of Norway|Al]]
  • Ligatures are separated: e.g. Æsir: [[Category:Norse mythology|Aesir]]
  • Sometimes which is appropriate depends on the language e.g.:
    • From the Bruno K. Öijer article: [[Category:Living people|Oijer, Bruno K.]]. From the Ötzi the Iceman article:[[Category:Mummies|Oetzi the Iceman]] (in this case the German umlaut on the O is expanded to an "e" - preferably only omit the diacritic, without applying foreign rules that could make collation seem illogical in English: [[Category:Mummies|Otzi the Iceman]].
    • From the Arne Åhman article: [[Category:Swedish athletes|Ahman, Arne]]. From the Lasse Åberg article: [[Category:Swedish film directors|Aaberg, Lasse]] (Contrary to the previous example the "Å" is here expanded to "Aa" - again, better to only omit the diacritic, to avoid collation confusion in English: [[Category:Swedish film directors|Aberg, Lasse]].

Year categories

See also wikipedia:naming conventions (numbers and dates)#Articles on other standard time periods

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 [[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]].
• The article about the year itself, 2004, should be sorted first among all articles by using [[Category:2004|*]].
• Articles for individual months, such as October 2004, should be sorted chronologically in the first section on the category page, in this case using [[Category:2004|*2004-10]].

Interlanguage links to categories

Interlanguage links work just as they do for regular articles; [[de:Kategorie:Mathematik]] 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 the different languages may have adopted different standards and practices for categorization, so a given category might not exist in other languages.

Tools

• 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 bugzilla and list them below.

(Bugs higher than 1775 have not been checked)

Redirects

• Redirects do not work properly with Categories duplicate
• Categories need piping feature to list by alternative name (to show redirects next to the articles they redirect to in categories, when appropriate)
• Redirect to category page doesn't work fixed!
• Problem categorizing redirects
• Would like the ability to list an article under multiple names in its categories duplicate
• Category tag on redirect pages does not work fixed!

Special:Categories

• Special:Categories:Add the number of articles in the category fixed!
• Link to Special:Categories should be customisable
• Special:Categories should be paged by letter, like Special:Allpages
• Special:Categories don't display categories with no article fixed!

Large categories

• Dealing with large categories
• On paged categories, article totals and subcat totals are incorrect
• Subcategory paging is not separate from article paging
• Table of contents for Categories

Updating problems

• Slow deletion of members from categories
• changes to links in a template do not update 'links', 'categorylinks', etc for pages including it

General

• Images inappropriately added to categories fixed
• Category and interwiki tags produce ugly whitespace fixed
• Add anchor tags to the headers used on category pages
• Special:Recentchangeslinked for particular categories fixed
• Characters in category names
• uncategorized pages report speedup hack
• Categories need to be structured by namespace
• Categories link at bottom of article points to wrong place duplicate
• Feature request: Special random category page fixed
• Ability to filter user contributions by time (e.g. "January 2003") or category
• Different new page text for each namespace (enhancement) (the text you get for completely and partly empty category pages, category talk pages, etc.) fixed
• Pluralization in listing totals fixed
• syntax such that a (template) page can be un-categorized, but still categorise pages transcluding it fixed
• feature request: "newest changes" display for categories, "start from" ... input mask duplicate
• syntax to transclude a page without the containing page inheriting categories, interlanguage links
• Category page listings have unbalanced columns
• automatic edit summary for categorizing pages
• RSS feed for category updates
• Whitelist doesn't work correctly for categories
• Feature request: boolean search in categories
• Page move updates categories with sorting tweak
• Unstable categories (non-ASCII characters) invalid
• New page created, db lag, result in double entries in categories fixed
• Category list missing on edit page fixed
• Feature request: Category reverse sort by date
• Subpages don't work in Help_talk: and Category_talk: fixed
• Korean wikipedia's categories need new sectioning scheme
• Ability to watch all articles in a category
• can't edit the history versions of the categories!
• Request: parameters in categories
• "No subcategories" display - I consider it a bug, not submitted.