| advertise add site services publishers database health videos | ![]() | about toolbar stats live show health store more stuff JOIN/LOGIN |
Infectious Substance, Category A and Biological Substance, Category B -... mayomedicallaboratories.c... | Doctor Eugene Lipov, M.D. - Biography and Wikipedia Entry eugenelipovmd.org | Tubal Reversal Information on Wikipedia tubal-reversal.net |
For a quick answer about categories, see Wikipedia:FAQ/Categorization. For more detailed technical information, see: Help:Category. For rules on how to name categories, see Wikipedia:Naming conventions (categories). Multiple shortcuts redirect here, you may be looking for: WikiProject Cats, WikiProject Categories or Help:Sorting.
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, allowing easy navigation between connected subject areas via a tree-like structure. This helps readers find articles on particular topics even if they don't know which articles exist or what they are called.
Quick summaryMain article: Wikipedia:FAQ/Categorization Linking [[Category:Name]] in the wikitext of any editable page causes that page to be categorized into a category called Name. This link will not display in the text, but will appear in a "Categories" box at the bottom of the page. (The link will be red if such a page is not yet created.) By convention these category declarations are placed near the end of the wikitext, before any stub templates (which themselves generate categories) and interlanguage links (which always go last). The category page is itself an editable page. Its wikitext describes the category, and will appear at the top. Below that a category page has a special, what links here, display mode to render a list of all the pages that have been placed in the category. If a linked-in page is also a category page, then it is a subcategory; these are listed below its wikitext. Otherwise it is treated as a member page of the category; these are rendered at the bottom. The section Display of category pages, below, will discuss how to control the sorting of the displayed categories. A category page is a page in the Category: namespace, and will not render as a visible link as usual. If you need to render a visual link to a category page, prefix a colon to the namespace word Category: as in [[:Category:Music]]. The display and piping of such a marked link ignores the initial colon. It appears as Category:Music, creating a one-way link to a category page while defeating the what links here mechanism that includes the page as a member page. The category systemWikipedia's categories form a hierarchical structure, consisting in effect of overlapping trees. (Because subcategories can have more than one immediate parent, the system as a whole is not a tree, but rather approximates a directed acyclic graph.) Categories are of two basic types:
It is also possible to combine the two types, to create list-and-topic categories. For example, Category:Voivodeships of Poland contains articles whose subjects are voivodeships, as well as articles relating to voivodeships in general. If the articles of one category logically also belong to another category, then the first category is made a subcategory of the second. So for example, Category:Musicians might be made a subcategory of Category:Music (by adding [[Category:Music]] to the text of the page Category:Musicians – not the other way round). Notice that it is unlikely for a topic category to be a subcategory of a list category. If B is a subcategory of A, then A is said to be a parent category of B. Many topic categories are of the type called eponymous categories, i.e. they correspond to a main topic article of the same name. For details on how to treat these, see Eponymous categories below. A page need not be added explicitly to all of the categories that logically contain it: normally a page (or subcategory) would not be added explicitly to a category if it is contained in one of that category's subcategories. However there are quite common exceptions to this: see Duplicate categorization rule below. Categorizing pagesEvery Wikipedia article should belong to at least one category. Similarly every category (except Category:Contents, which is the root of the hierarchy) should be placed in at least one parent category. 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. 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. 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. Eponymous categoriesOften 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 createdCategories 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. SubcategorizationAlthough 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 ruleIf 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:
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 pagesForm of entriesThe 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 orderIt 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 keysTo 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, If a page is to be given the same sort key in all or several of its categories, the 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, {{PAGENAME}} 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
Split displayWhen 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:
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 descriptionRather 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 categoriesThe 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 pagesUser 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. ImagesImages 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 categoriesIn 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 __HIDDENCAT__). 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 templatesSee also: Wikipedia:Category suppression 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.
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 {{PAGENAME}} 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 categoriesAlthough 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. 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 categoriesInterlanguage 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 different Wikipedias may have adopted different standards and practices for categorization, so not all categories have equivalents in other languages. TipsDisplaying category contents on pagesTo 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
to display just the subcategory tree, and
to display member pages as well. Retrieving category informationRaw 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 categoriesOutside mainspace, the following templates can be used to display a category in different ways, or link to its maintenance pages.
Searching for articles in categoriesIn 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
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
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
| |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| ↑ top of page ↑ | about thumbshots |