Wikipedia:Categorization/rewrite

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Note: This page was used for the rewrite of Wikipedia:Categorization. On January 17, 2006 this page was copied there.

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.

Contents

[edit] 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.

[edit] Guidelines

[edit] 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 Oscar. 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 exists. 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.
  9. If you don't know where to put an article don't worry about it. Instead of adding a category, use the {{catneeded}} tag to bring attention to the article. Editors who love to categorize articles will find a good home for your article.

[edit] 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.

[edit] 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.

[edit] 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.

[edit] 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 ...

[edit] How to put an article into categories

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

[edit] 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.

[edit] 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). 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.

[edit] 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.

[edit] 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.

[edit] Organizing categories

[edit] Large categories

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).

[edit] 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:

  • 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.

[edit] Other requirements

[edit] 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.

[edit] 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.

[edit] Image namespace

See categorizing images.

[edit] 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.

[edit] 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.

[edit] 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 [[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:

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. Using a space after the pipe is the customary way to categorize an article in a category with the same name. For an example, see Category:Suspension bridges.

[edit] 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 [[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]].

[edit] 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.

[edit] 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.

[edit] Current projects

See: Wikipedia:Categorization projects (current)

[edit] Known category-related bugs

Please report new category-related bugs on bugzilla and list them below.

(Bugs higher than 1775 have not been checked)

[edit] Redirects

[edit] Special:Categories

[edit] Large categories

[edit] Updating problems

[edit] General

[edit] See also

[edit] Browsing categories

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