Wikipedia:Categories, lists, and navigation templates

Wikipedia offers several ways to group articles: categories, list articles (including item lists, as well as topical glossary, index, outline, and timeline articles), other lists including embedded lists, and navigation templates (of which article series boxes are one type). The grouping of articles by one method neither requires nor forbids the use of the other methods for the same informational grouping. Instead, each method of organizing information has its own advantages and disadvantages, and is applied for the most part independently of the other methods following the guidelines and standards that have evolved on Wikipedia for each of these systems.

Accordingly, these methods should not be considered in conflict with each other. Rather, they are synergistic, each one complementing the others. For example, since editors differ in style, some favor building lists while others favor building categories, allowing links to be gathered in two different ways, with lists often leapfrogging categories, and vice versa. This approach has resulted in two main link-based systems of navigating Wikipedia. See the navigation menu at the top of Contents, and see Category:Wikipedia categories. Many users prefer to browse Wikipedia through its lists, while others prefer to navigate by category; and lists are more obvious to beginners, who may not discover the category system right away. Therefore, the "category camp" should not delete or dismantle Wikipedia's lists, and the "list camp" shouldn't tear down Wikipedia's category system—doing so wastes valuable resources. Instead, each should be used to update the other.

At the same time, there may be circumstances where consensus determines that one or more methods of presenting information is inappropriate for Wikipedia. For instance, the guideline on overcategorization sets out a number of situations in which consensus has consistently determined that categories should not be used. A regularly occurring outcome at WP:CFD for some deleted categories is to listify, because there are cases where lists are appropriate while categories may not be (e.g. List of unusual units of measurement exists as a list, but not as a category ).

Category workers, list builders and outline builders, and series box designers all endeavor to develop comprehensive networks of links for navigating the encyclopedia. Because of this, increasingly, multiple entries to fields of knowledge are being provided. Take "symphonies", for example:
 * Categories: Category:Symphonies
 * Lists: List of symphonies with names
 * Navigation Templates: Template:Symphonies by number and name

Overlapping categories, lists and navigation templates are not considered duplicative
It is neither improper nor uncommon to simultaneously have a category, a list, and a navigation template that all cover the same topic. These systems of organizing information are considered to be complementary, not inappropriately duplicative. Furthermore, arguing that a category duplicates a list (or vice versa) at a deletion discussion is not a valid reason for deletion and should be avoided. Redirects of list articles to categories are highly discouraged: list articles should take the place of the redirect.

Consider that lists may include features not available to categories, and building a rudimentary list of links is a useful step in improving a list. Deleting these rudimentary lists is a waste of these building blocks, and unnecessarily pressures list builders into providing a larger initial commitment of effort whenever they wish to create a new list, which may be felt as a disincentive. When deciding whether to create or avoid a list, the existence of a category on the same topic is irrelevant.

Below is a comparison of how these techniques group information and the advantages and disadvantages of each.

Categories
Compared to a list, a category may have both advantages and disadvantages.

Example of a category page. Every page in the article namespace should have 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:American pop singers
 * Not useful: Category:Musicians whose first name starts with M

A category is probably inappropriate if the answer to the following questions is "no":
 * Is it possible to write a few paragraphs or more on the subject of a 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?

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.

An article should usually not be in both a category and its subcategory, e.g. Microsoft Office is in Category:Microsoft software, so should not also be in Category:Software—except when the article defines a category as well as being in a higher category, e.g. Ohio is in both Category:States of the United States and Category:Ohio (a good way to understand this exception is that if an article exists, and then a category is created on the same subject as the article, it should not cause the article to be removed from any of its categories).

Exceptions should also be considered when the article subject has a relevance to the parent category that is not expressed by the subcategory's definition. For instance, if Category:People executed by guillotine during the French Revolution was the only subcategory of Category:People of the French Revolution, it would not make sense to remove major figures of the French Revolution solely because of the means of their death.

Categories appear without annotations, so be careful of neutral point of view (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. Especially see Categorization of people.

An exception to the above rules is Category:Wikipedia maintenance, which contains categories intended to be temporary.

Every category should be a subcategory of some other category. You can start from the top of the articles category hierarchy at Category:Main topic classifications. If you think a good parent probably exists but you just can't find it, add the Uncategorized tag. Your category will show up at Special:Uncategorizedcategories.

Categories have sort keys like other pages, although they are used in a more flexible fashion. See WP:SORTKEY for technical considerations.

For articles without any stable category, the Uncategorized tag can be used to bring attention to it, either on its own, or in the format. There is also an automatically updated list at Special:Uncategorizedpages which displays uncategorized/stubbed articles; however, it only updates once every few days, and only lists 1000 articles at a time. So it is always best to explicitly place an uncat tag, if you are uncertain how an article should be categorized.

Advantages of a category

 * 1) Auto-linking. Create a link to a category on an article page, and a corresponding link to that article will be visible on the category page.
 * 2) Multi-directional navigation. A category can contain multiple subcategories, and can also be part of several categories. Categories are organized within Wikipedia into a web of knowledge starting with Category:Wikipedia categories.
 * 3) Good for exploratory browsing of Wikipedia.
 * 4) Less susceptible to external linkspam than other types of pages, because only Wikipedia articles can be members of categories.
 * 5) Relatively unobtrusive in that they generally don't distract from the flow of the article.
 * 6) Search can use the incategory parameter to exclude or include all pages in that category. Subcategories are not included, but multiple terms can be added.

Disadvantages of a category

 * 1) Can't be edited directly to add or remove entries. This must be done at the bottom of each article to be included or excluded from the category.
 * 2) Categories only show the page name of each page being categorized. So while the category description of the category may provide broader information, individual category members cannot be annotated with descriptions or comments, so they give no context or elaboration for any specific entry.
 * 3) There is no provision for referencing any specific entry, to verify a page meets a category's criteria of inclusion.
 * 4) Entries are arranged in alphabetical order only (though you can control the alphabetization). They cannot be organized into sections and subsections on a single page, each with its own descriptive introduction.
 * 5) Can be difficult to maintain:
 * 6) A category with hundreds of items cannot be moved except by editing hundreds of articles (though a bot can help)
 * 7) Tracking changes to a category is difficult because a category's edit history does not show when entries were added or removed from the category. So there is no easy way to tell when an article is removed from a category—it simply disappears with no indication that it was ever there in the first place. Wikipedia's watchlist feature does enable a user to watch a category for category membership changes.
 * 8) Does not support other forms of tracking, such as adding red links. (Red links are useful as gap indicators and as task reminders to create those articles.) However, stubs can be added to categories.
 * 9) Alternative names for the same item can be included only by including redirects in the category.
 * 10) It is not obvious to new users that categories exist, how to add items to them, how to link new categories into existing schemes, nor how to deal with point of view (POV) concerns.
 * 11) Categories are not shown in mobile view.
 * 12) Display of items in a category is limited to 200 on a page. To see the full contents of a category with more members than this, multiple pages need to be viewed.

Lists
Compared to a category, a list may have both advantages and disadvantages.

Example of a list: List of dog breeds

Advantages of a list

 * 1) Good for exploratory browsing of Wikipedia.
 * 2) Often more comprehensive because each is maintained from a centralized location (at the page itself).
 * 3) * See the top end of the list hierarchy at Lists of topics, Lists of basic topics, List of overviews, and List of glossaries.
 * 4) Can be formatted in many different ways, to improve the presentation of the contents of the list.
 * 5) * For example, several levels of a hierarchy may be included in a list, or the list may have multiple columns, each of which can be a basis for the user to sort the list.
 * 6) Can be built and maintained by editing a single page, whereas filling a category requires the editing of multiple pages.
 * 7) Can be embellished with annotations (further details).
 * 8) * For example, a list of soccer world championship teams can include with each entry when each championship was won, whom the champions defeated, who their coach was, etc.
 * 9) Included in searches of Wikipedia. Being in the main namespace, lists are included by default in Wikipedia searches. Their content is also searched by Google and other search engines.
 * 10) Can be referenced to justify the inclusion of listed articles.
 * 11) Can include unlinked items
 * 12) * For example, List of compositions by Franz Schubert, or, if appropriate, red links. See WP:Write the article first.
 * 13) List items can be manually sorted using a variety of methods. An article can appear several times or in different ways in the same list.
 * 14) List items can be linked to specific sections of articles.
 * 15) Can include invisible links to discussion pages, so that clicking on "related changes" will include those (Format:   ); the list itself can also be included by linking it to itself, e.g. by linking the bold-faced phrase in the lead:
 * 16) Can be more easily edited by newbies who are less familiar with Wiki markup language.
 * 17) Images can be interspersed throughout a list.
 * 18) Templates (such as navigation boxes) can be included as portions of a list.
 * 19) An embedded list, one incorporated into an article on a topic, can include entries which are not sufficiently notable to deserve their own articles, and yet may yet be sufficiently notable to incorporate into the list. Furthermore, since the notability threshold for a mention is less than that for a whole article, you can easily add a mention to a list within an article, without having to make the judgment call on notability which you would need to make if you were to add a whole article—if someone else feels that it is notable enough, they can always linkify the mention and create an article anyway.

Disadvantages of a list

 * 1) No auto-linking. Every article links to its categories in a consistent way, but lists may be more difficult to discover because not every article listed links to it, and each may choose to link to it in a different way. Attempting to enforce crosslinks from articles in the category is error-prone, makes editing the list taxing, and counteracts the ease-of-editing benefits lists otherwise enjoy.
 * 2) Less comprehensive hierarchy. The category system has an extensive and detailed hierarchy to facilitate browsing by increasing specialization, while lists of lists are relatively rare and are not deeply nested.
 * 3) Complex automated processing. Lists are more difficult to process automatically using bots, because they may contain prose that contains links to items that are not in the list itself, and it is necessary to parse the page wikitext to extract listed items instead of using a specialized API as categories do.
 * 4) No automatic sorting. Editors have to manually determine where an entry belongs, and add it there. Often editors will simply add new items to the bottom of the list, reducing the list's effectiveness. This disadvantage can be overcome by placing the list in a sortable table.
 * 5) Can become bogged down with entries that cannot be reliably sourced and do not meet the requirements for inclusion in the encyclopaedia.
 * 6) Some topics are so broad that a list would be unmanageably long and effectively unmaintainable.
 * 7) * For example, a list of all people from a particular country who have Wikipedia articles

Navigation templates
Navigation templates are a grouping of links used in multiple related articles to facilitate navigation between those articles in Wikipedia. Navigation templates are generally presented in one of two formats:
 * Horizontal, placed at the bottom of articles and also called navboxes
 * Vertical, often found at the top-right corner of articles and called sidebars

Wiki markup documentation for navigation templates at different levels of specificity includes Template:Navbox/doc, Template:Sidebar/doc, and, at the top or bottom of the template, Template:Navbar/doc.

Each link should clearly be identifiable as such to our readers. In general, text colors should be consistent with Wikipedia text color defaults, so links should be blue ; dead links should be red ; and red and blue should not be used for other (non-link) text. However, specific navbox guidelines for color of text and background other than the defaults are available.

Navigation templates are particularly useful for a small, well-defined group of articles; templates with a large number of links are not forbidden, but can appear overly busy and be hard to read and use. Good navboxes generally follow most or all of these guidelines:
 * 1) All articles within a template relate to a single, coherent subject.
 * 2) The subject of the template should be mentioned in every article.
 * 3) The articles should refer to each other, to a reasonable extent.
 * 4) There should be a Wikipedia article on the subject of the template.
 * 5) If not for the navigation template, an editor would be inclined to link many of these articles in the See also sections of the articles.

If the collection of articles does not meet these criteria, the articles are likely loosely related. A list, category, or neither, may accordingly be more appropriate.

Do not rely solely on navboxes for links to articles highly relevant to a particular article, or override the "image=" field to illustrate something from the article. Navboxes are not displayed on the mobile website for Wikipedia, which accounts for around half of readers. (See Phabricator ticket for progress on the mobile issue.)

Navigation templates located in the top-right corner of articles (sometimes called a "sidebar" or "part of a series" template) should be treated with special attention, because they are so prominently displayed to readers. The collection of articles in a sidebar template should be fairly tightly related, and the template should meet most or all of the preceding guidelines. If the articles are not tightly related, a footer template or navbox, located at the bottom of the article, may be more appropriate. The placement of sidebars in an article lead is discouraged by MOS:LEAD (though they may be permitted on a case-by-case basis).

The article links in a navigation template should be grouped into clusters, by topic, or by era, etc. Alphabetical ordering does not provide any additional value to a category containing the same article links. For example, see Template:General physics which has articles grouped into related sub-topics.

Every article that transcludes a given navbox should normally also be included as a link in the navbox, so that the navigation is bidirectional.

The use of navigation templates is neither required nor prohibited for any article. Whether to include navboxes, and which to include, is often suggested by WikiProjects, but is ultimately determined through discussion and consensus among the editors at each individual article. Per the bidirectionality principle above, this may also affect inclusion of a particular article in a navigation template. If a disagreement should arise, please centralize discussion at the article talk page, not that of the template (which may be watchlisted mostly only by template coders).

Avoid adding performances of entertainers into the navboxes for the productions that they appeared in, or crew members into navboxes for the productions they worked on. This includes, but is not limited to actors/actresses, comedians, television/radio presenters, writers, composers, etc. This avoids over-proliferation of navigation templates at the bottom of performers' articles, and avoids putting undue weight on certain performances of an entertainer over others.

Filmographies (and similar) of individuals should also not be included in navboxes, unless the individual concerned could be considered a primary creator of the material in question. This avoids over-proliferation of individuals' navboxes on each production's article, and avoids putting undue weight on the contributions of certain individuals over others.

Finally, external links should not be included in navigation templates. Sources may be included in the template documentation (a section that is visible only after viewing the template itself, but not upon its transclusion).

Advantages

 * 1) Provides a consistent look and navigation system for related articles.
 * 2) Faster to navigate than a category.
 * 3) Gives immediate information to equivalent elements
 * 4) For presenting a series of articles in a chronological order, a template is often most appropriate. Example: Template:Princess Royal (there are two Marys and two Annes in that list, which makes the chronological way of presenting these princesses an asset to a merely alphabetically ordered presentation of these same names). For very long chronological series, it is preferable to use succession boxes, which only show the elements of the series immediately preceding and succeeding the article.
 * 5) They provide an organized resource for readers who went through an article in some broad topic to find other articles on the same broad topic, rather than making those readers "go fish" for articles wiki-linked in the text or in the "See also" section.
 * 6) Mitigates large "See also" sections, potentially duplicated and out-of-sync among related articles

Disadvantages

 * 1) Not shown to readers using the mobile web site.
 * 2) Does not provide a consistent look and navigation system between different topics—there is no single format across all navigation templates.
 * 3) If simple, can often be replaced with a category. It also can be difficult to give more detail than a category can give without the box becoming unmanageably large.
 * 4) Can become ugly or seem pointless, e.g. by unsightly coloring schemes, size, number of them on the same page, etc. For this reason article series boxes need to be self-evident, while they can't contain much text for definitions or explanations.
 * 5) Inclusion of article links or subdivisions in a template may inadvertently push a point of view. It may also incorrectly suggest that one aspect of a topic or a linked example is of more, less, or equal importance to others; be used to advertise obscure topics in prominent places; or assert project proprietorship. Templates can go to Templates for discussion if they appear to push a POV. Trying to remedy this by adding more templates might lead to the disadvantage described in the previous point.
 * 6) On the other hand, may not give the reader enough clues as to which links are most relevant or important when this would not be controversial
 * 7) Can take up too much space for information that is only tangentially related
 * 8) Includes the full list of links in every article, even though often many of the links are not useful in some of the articles
 * 9) Due to size, the use of multiple nav templates may take up too much space on one article, which could lead to a POV-tainted choice as to which to include. This can be minimised by setting all or most templates on a page to autocollapse, hiding most of their content until activated.
 * 10) Templates are not included in search results by default, which makes it hard for readers and editors to find them.
 * 11) They implicitly assume that readers who went through an article in some broad topic will want to read other articles on the same broad topic, rather than articles wiki-linked in the text or in the "See also" section.

Sidebars have some specific issues and should be treated with special attention, because they are so prominently displayed to readers:
 * 1) The large chunk of highly visible screen space might be better used for images or essential information.
 * 2) They might be perceived as fencing off a subject as the "territory" of a particular scholarly area.
 * 3) The collection of articles in a sidebar template should be fairly tightly related, and the template should meet most or all of the preceding guidelines. If the articles are not tightly related, a navbox may be more appropriate.

Examples
Example templates include:
 * Template:Spain topics (medium-sized horizontal template)
 * Template:Philosophy topics (large horizontal template)
 * Template:Philosophy sidebar ("Part of a series on ..." vertical template)
 * Template:Policy list (a small vertical template)
 * (several horizontal templates at the bottom of an article)

Some unusual templates include:
 * Template:Administrators' noticeboard archives (a vertical template)
 * Template:Noticeboard links (a horizontal template sometimes positioned at the top)
 * Template:Harry Potter (an example of organizing voluminous, diverse material into a readable template)