Academic Kids:Categorisation FAQ
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Frequently asked questions about the Wikipedia Category feature.
For a quick introduction to categories, see Wikipedia:Category. For guidelines on creating and organizing categories, see Wikipedia:Categorization.
What are categories?
Categories allow articles to be placed in one or more groups, and allows those groups to be further categorized.
When an article belongs to a category, it will contain a special link to a page that describes the category. Similarly, when a sub-category belongs to a parent category, it will contain a special link to the parent category's page.
Each category page contains an introduction that can be edited like an article, and an automatically-generated list of links to sub-categories and articles that belong to the category.
The software feature does not force a strict hierarchy or tree of categories, but allows multiple categorisation schemes to co-exist simultaneously. Because each article can appear in more than one category, and each category can appear in more than one parent category, the categories do not form a tree structure, but a more general directed graph. It is even possible to construct loops in the category graph, but this is seldom a good idea.
See Wikipedia:Category and Wikipedia:Categorization.
What is the state of the feature?
The category feature appeared in the MediaWiki software v1.3, which was implemented on Wikipedia in late May 2004.
Initially categories were displayed at the top right of articles, but they were soon moved to the bottom due to layout conflicts.
Known issues
Reported categorisation bugs (http://bugzilla.wikimedia.org/buglist.cgi?query_format=advanced&short_desc_type=allwordssubstr&short_desc=&product=MediaWiki&component=Categories&bug_status=UNCONFIRMED&bug_status=NEW&bug_status=ASSIGNED&bug_status=REOPENED&bugidtype=include&chfieldfrom=&chfieldto=Now&cmdtype=doit) can be seen at MediaZilla (http://bugzilla.wikimedia.org/). See also: Wikipedia:Categorization#Known_category-related_bugs.
- Category pages still show old sub-categories and articles after edits [1] (http://sourceforge.net/tracker/index.php?func=detail&aid=970584&group_id=34373&atid=411192) [2] (http://sourceforge.net/tracker/index.php?func=detail&aid=975072&group_id=34373&atid=411192).
- Work-around: You need to make a dummy edit to the category page to fix this, e.g., add a space at the end of a line. Explain this in the edit summary (e.g. "Dummy edit to refresh"), and flag the edit as minor if you have a Wikipedia user account.
- Categories can be sub-categories of themselves [3] (http://sourceforge.net/tracker/index.php?func=detail&aid=970259&group_id=34373&atid=411192).
- Work-around: Don't do it.
- Categories cannot be redirected [4] (http://bugzilla.wikimedia.org/show_bug.cgi?id=100).
- Work-around: Don't do it, place a link on the page instead if it already exists.
- Layout issues:
- Work-around: Edit category pages so that there is only one category tag per line.
What is the state of categorisation?
When trying to categorise an article, it is still difficult to tell into which categories it should be placed, and when trying to categorise by a field of interest, one is likely to intersect someone else's efforts from another field.
Category policies are still being determined through experimentation, discussion, and polls. Categorisations and systems are likely to be discussed and improved upon for a very long time.
What is the purpose of categories?
There are two main ways to use categories: lists and topics. When starting a subcategory, making an early decision about whether it is a list or a topic will reduce later renames, recategorizations, and discussions. The category page can be used to tell others whether it is a list or a topic, and to link to a main list or article in the normal Wikipedia:namespace.
See meta:Categorization requirements for the original purpose of the feature, and Wikipedia:Categorization for current usage and guidelines for assignment.
Categories as lists
Grouping articles into a category is not the same as making a list of articles. When you make a list of articles, you edit the list directly; but when you place articles into a category, you simply edit the articles, and a list of articles is automatically created on the category's page.
Despite the difference in how they are maintained, it is sometimes convenient to think of a category as a list of articles.
While an article may be in multiple lists, the goal is that browsing downwards from a list parent category, e.g. Category:Cities, should only arrive at articles that are cities, e.g. London, and not related articles e.g. History of London. See the John Lennon example.
There are some natural hierarchies of lists. One example is the scientific classification of organisms, which would only place an article in one category. Other systems use multiple listings, e.g. Wikipedia could be in [[Category:Wikis]] and Category:Encyclopedias.
List categories are likely to also be subcategories of topic categories.
Currently MediaWiki does not have a facility to look at a category such as Category:Religious texts and (recursively) retrieve a list of all articles in sub-categories.
Related topics
To allow related articles to be grouped together, and those groupings placed into a hierarchy. For example, both London and History of London could be in the category London.
There are some natural hierarchies of topics, e.g., placing Category:European history under Category:Europe and Category:History.
Topic categories are unlikely to be subcategories of list categories.
Currently the software does not allow you to look at Category:People and retrieve a list of all articles in sub-categories.
Can pages be in more than one category?
Yes, it is expected that most pages will be members of more than one category.
In exactly the same way, each category can be a member of more than one parent category.
How can I see the categories of a page?
Categories are shown at the bottom of a page. If you cannot see them, the page has no categories.
What is the naming convention for categories?
Use the Wikipedia titling conventions of no unnecessary capital letters or abbreviations, i.e. use [[Category:Category examples]] instead of [[Category:Category E.g.]]. Avoid ambiguities.
Lists
If the category is used like a list of articles, then avoid the word List in the name of the category, and use plurals, e.g. Category:Popes.
However, if the category is used like a list of lists, then using the word Lists in the name of the category is appropriate, e.g. Category:Lists of radio stations.
Topics
Use the topic name without indicating structure, e.g. [[:Category:History of London]] instead of [[:Category:History - Europe - UK - London]].
Editing
How do I place an article in categories?
Edit the article and add [[Category:Category examples]].
How do I place a category in parent categories?
Edit the category page and add [[Category:Examples]].
How do I reference a category on a page without categorising the page?
To link to the category page, put a colon at the front, e.g. [[:Category:Category examples]].
Where should the category tag go in the article?
At the bottom of the article after the appendices. They are mostly placed before the inter-wiki language links, but some people prefer to place the category tags at the very bottom.
This ensures that when newcomers press "edit", they are immediately presented with the main article text, rather than the more esoteric links.
See past placement discussion and poll.
How do I sort the article differently on the category page?
Use a "pipe-trick". For example, to sort Pope Gregory IX after Pope Gregory VIII on Category:Popes under G, use the syntax [[Category:Pope Gregory IX|Gregory 09]] on the article pages. The extra text is only used for sorting and is not displayed.
It is sometimes desirable to force the most important articles or sub-categories to appear at the beginning of the sorted list on a category's page. To do this, use an asterisk or a space as the sort key. For example, [[Category:Whatever|*]] or [[Category:Whatever| ]]. Some other special characters are also occasionally used for this purpose, and there is no consensus on what is best.
Somebody changed my categorization - what do I do?
All contributions to Wikipedia may be "edited mercilessly". If the change was not explained in the article history or talk page, try leaving a question on the relevant user's talk page. If you have a Wikipedia user account, they will respond on your talk page rather than their own.
I want to change the relationships of some categories - will anyone mind?
If you want to restructure some existing categories, it is best to discuss your plans with others working in the same areas, or at least to announce your intentions. This is to avoid the situation where someone is placing an article into multiple categories, someone else else is populating a category with multiple articles and parent categories, while someone else is trying to restructure part of the category tree, and nobody ends up with what they want. A good place to start looking for an interested group of people is Category:WikiProjects.
What goes on a category page?
Category pages exist to be a convenient cross-reference to related articles and other categories. A category page should contain a brief description of the purpose of the category. A prominent link to the most important article in the category is usually a good idea, but please avoid copying large quantities of text or images from an article to a category page.
Are "List ..." articles still needed?
There are many articles in Wikipedia called "List of ...", e.g. "List of assassins". Lists are still useful for showing "missing" articles. See also: Wikipedia:Categories, lists, and series boxes, Wikipedia talk:Categorization/Archive 1#Lists v. categories and Category:Lists that should be categories.
Are topic and hierarchy info-boxes still needed?
Many articles have "info-boxes" -- side-boxes or footers linking to other articles and lists, sometimes using Wikipedia:Templates. Some of these are listed at Wikipedia:Navigational templates. While some info-boxes are made redundant, others have useful grouping of the cross-references that cannot be done with categories. See also: Wikipedia:Categories, lists, and series boxes, Wikipedia:Article series, Wikipedia:Incumbent series, Wikipedia:Topics.
I am interested in XYZ categories - where can I get involved?
See Wikipedia:Categorization#Current projects, Wikipedia:WikiProject and Wikipedia talk:Category schemes.
What categories already exist?
Wikipedia:Category schemes shows designs that predate the category feature. Category:Fundamental shows top level projects. Category:Main page has one scheme for organising topics, which relates to the Wikipedia main page. Some high-level categories can be found at Wikipedia:Categorization#Current projects. A list of all categories can be found at Special:Categories.
Do categories need parents?
Yes. Top-level categories go in Category:Fundamental. If the category is not fundamental, use Category:Orphaned categories temporarily.
Can categories be renamed, moved, or redirected?
Yes, "speedy renaming" can be done by listing the category on Wikipedia:Categories for deletion#Speedy renaming. See Wikipedia:Categories for deletion policies#Speedy renaming procedure.
How do I delete a category?
By listing the category on Wikipedia:Categories for deletion. See Wikipedia:Categories for deletion policies.
Which categories can be used for categorisation of articles on people?
Articles about people should be categorised cautiously. Unlike the body of the article, the various category choices for people can focus on what, in most cases, are common and unrelated attributes such as place of birth and gender, instead of emphasising the reason for their inclusion.
See Wikipedia:Categorization of people for guidelines.
How else can I navigate articles?
As well as the standard links within articles themselves, every page has a link (typically at the side) called What links here.
How do I report feature bugs?
Bugs should be reported to the MediaZilla (http://bugzilla.wikimedia.org/) website. (See Wikipedia:Bug reports for instructions.)
How do I request feature enhancements?
Enhancments can be requested at the MediaZilla (http://bugzilla.wikimedia.org/) website. (See also meta:MediaWiki roadmap and Wikipedia:MediaWiki future directions.)