Commons:Categories

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This page is considered anofficial policyon Wikimedia Commons.

It has wide acceptance among editors and is considered a standard that everyone must follow. Except for minor edits (such as fixing typos, or bringing information up to date), please make use of thediscussion pageto propose changes to this policy.

Acategoryis a software feature ofMediaWiki,a special page which is intended to group related pages and media. In practice, it implies that you'll associate a single subject with a given category. The category name should be enough to guess the subject, but some extra text can be useful to precisely define it. Thecategorystructure is the primary way to organize and find files on the Commons. It is essential that every file can be found by browsing the category structure. To allow this, each file must be put into a category directly. Each category should itself be in more general categories, forming a hierarchical structure.

Quick guide

1. How to find the appropriate categories

  • Find categories with the search engine (see#Categorization tips)
  • or check how similar files are categorized (some may not be categorized though)
  • or start from the main topical category (Category:Topics)
  • Starting from these categories, check their parent or sub-categories to find an appropriate category. Avoid picking too general categories.

2. Add the categories to the file

Category structure in Wikimedia Commons

Principles

Shortcut

The main principles are:

Hierarchic principle

The category structure is (ideally) amulti-hierarchywith a single root category,Category:CommonsRoot.All categories (exceptCommonsRoot) should be contained in at least one other category. There should be no cycles (i.e. a category should not contain itself, directly or indirectly).

Modularity principle

The page (file, category) should be put in the most specific category/categories that fit(s) the page (not directly to its parent categories). A category can have more parent categories. A category can combine two (or more) different criteria; such categories are called "compound categories" or "intersection categories". E.g. the root categoryCategory:Churchesand the root categoryCategory:Russiahave a common subcategoryChurches in Russia.

Simplicity principle

This principle suggests not to combine too many different criteria.

Selectivity principle

We should not classify items which are related to different subjects in the same category. There should be one category per topic; multi-subject categories should be avoided. The category name should be unambiguous and not homonymous.

Universality principle

Identical items should have identical names for all countries and at all levels of categorization. The categorization structure should be as systematical and unified as possible, and local dialects and terminology should be suppressed in favour of universality if possible. Analogic categorization branches should have an analogic structure.

Types of reflected relations

The category structure should reflect a hierarchy of concepts, from the most generic one down to the very specific. The structure uses and combines more types of relation, e. g.

  • Hyponymy:a sort/kind/type of… (typically in biological taxonomy)
  • Meronymy:a part of…, a member of… (typically for geographical division, building/room, device/component etc.)
  • Attributes:
    • Qualitative and general attributes (color, shape, size, ability or disability, nationality, technique, quality, awards…)
    • Location: where, in…, from… (place/event, place/building, place/exhibit, place/people, country/language, source/work, factory or country/product etc.)
    • Timing: when (time/event, time/depicted situation, time of birth, inception or construction, time of death, demolition or termination etc.)
  • Agentive and influence relations: (creator/work, device/product, company/product, discipline or profession/their subjects and terms, parent/children, subordination, owner/property, initiator/follower, subject/other subjects dedicated to it or named after it, subject/its duplicate, imitation, depiction or symbol etc etc.)
  • Modification: original/modified or modified/original (avoid cyclic structure) – renamed, rebuilt, repurposed or transformed subjects.

Major categories

The top-most categories (the ones contained directly in CommonsRoot) divide the category structure by the purpose of the contained categories:

  • Category:Topics– This category is the global common root of the media files categorized by the TOPIC. ALL media files should be categorized under this category for the sake of allowing others to find them by topic. Topical categories shouldn't be included through templates.
  • Category:Copyright statuses– This category is the global common root of the media files categorized by the 'LICENSE. ALL media files should be categorized under this category with the appropriatelicense tag.This type of category is added by including it in the templates.
  • Category:Media by source– This category is the global common root of the media files categorized by the SOURCE, where they come from (books, collections, sites, etc.). This type of category is generally added by template.
  • Category:Media types– This category is the global common root of the media files categorized by the Media TYPE. Please note that this type of categorization is sometimes omitted for images, since the vast majority of files on the Commons are images of some sort.
  • Category:Commons– This category is the global common root of categorizing Commons maintenance tasks and pages (Commons:-, and Help:-) except for media files. The translated pages in each language should be categorized under their language categories, using the "Category:Commons-ISO-LANGUAGE-CODE"style. The structure ofCategory:Commons-enis the sample hierarchy for every other language sub category. Do not use two colons in category or page names. Seethis discussionandHelp:Namespaces.
There is a sub categoryCategory:Commons maintenance content,which is for the special maintenance of Wikimedia Commons global common contents and which does not get translated. ALL media files should be categorized under the first 4 categories below, but ONLY files having problems and needing to be fixed should also be in the sub-categoryCategory:Commons maintenance content.
  • Category:User categories– this is for categories that contain Commons users' galleries, images and texts, sorted by things like the language they speak. This also contains theCategory:User galleries,which is for user specific (i.e. non-topic) galleries that don't need to be in English language.

How to use categories

You should always put your uploads into categories and/or gallery pages according to topic, so your contributions can be found and used by others.

It is rarely necessary to create a new category (there are exceptions, such as uploading a new text and seePeoplebelow). Before doing so, make sure you are familiar with the existing category structure, and with the customs and policies of the Commons. Please see if there exists acategory schemeor aCommons projectfor your topic, and follow the conventions described there.

Category names

Category names should generally be in English (seeCommons:Language policy). However, there are exceptions such as some proper names, biological taxa and names for which the non-English name is most commonly used in the English language (or there is no evidence of usage of an English-language version).Latin alphabetsare used in original form including diacritics and derived letters, non-Latin alphabets are transcribed to the English Latin script. Basic English characters (ISO/IEC 646) are preferred over national variants or extension character sets (for instance, 'straight' apostrophes over 'curly'), where reasonable.

Categories grouping subcategories by name should generally be named "by name" rather than "by alphabet" (e.g.Category:Ships by name).

We still lack internationalization for category names, but this issue should be resolved with appropriate changes to the MediaWiki software (seeT31928:Show translated titles per user language in categories too). Creating intermingled category structures in different languages would only make things worse.

For a general discussion of MediaWiki's category feature, see themanual page on categories.

Categorizing pages

To add a page (be it an image, a gallery page, or a category page) to a category, add the following code to the end of the page.

[[Category:Category name]]

For example, if you are uploading a diagram showing the orbit of comets, you could add the following to the image description page: 

[[Category:Astronomical diagrams]]
[[Category:Comets]]

This will make the diagram show up in the categoriesAstronomical diagramsandComets.

For information on how to find good categories for your uploads and galleries, read the sectionFind an appropriate categorybelow.

Creating a new category

To create a new category:

  1. Do a thorough search, to be sure there isn't an existing category that will serve the purpose.
  2. Find images (or a gallery or other pages) which should be put in the new category. Edit this page, and at the end insert the new category reference. e.g.[[Category:Title]].Save the edited page. The new category appears as a red link at the bottom of the page.
  3. Click on that red link. The new, empty, category page appears for editing. You can now edit the category like any other wiki page.

A category page should contain the following information (in order of importance):

  • Category-links that put it into one or more parent categories. At the bottom of the new page, insert lines of the form[[Category:Relevant categories]].
  • A short description text that explains what should be in the category, if the title is not clear or unambiguous enough on its own. Descriptions in particular languages can be tagged e.g. with the template{{ab|...}}for description in Abkhazian,{{en|...}}for description in English, etc., as listed inCommons:Language templates); or using the{{Multilingual description}}template to show only the description in the user’s preferred language if there is one.
  • Interwiki or interlanguage links to the article or category with the same topic in Wikipedia by adding the appropriate sitelinks on the corresponding Wikidata page. After creating the category page, click "Add links" under "In Wikipedia" on the bottom of the sidebar to the left to add them.

See also#How to categorize: guidance by topicfor guidance on specific classes of category, e.g. categories about#People.

Sorting categories

If a category should be sorted according to a different string than the category title, there are two ways:

Defining a sortkey (sort string)for allparent categories: 

{{DEFAULTSORT:sortkey}}
[[Category:Parent category A]]
[[Category:Parent category B]]
This will sort the category into all parent categories under the specified sortkey. For instance, the title of a category about a person would not be the right sort string. For such categories, insert just before the categories a line with the correct sort string like:
{{DEFAULTSORT:Lastname, Firstname}}

Defining a sortkey onlyfor oneof the parent categories: 

[[Category:Parent category A|sortkey]]
[[Category:Parent category B]]
This will also overrides any maybe defined DEFAULTSORT for ‘Parent category A’.

The default sort order on Commons is: 

░!"# $ % & ' ( ) * +, -. / 0 9:; < = >? @ A a Z z [ \ ] ^ _ ` { | } ~ É é 📚

→See also:Meta:Help:Sorting#Sort modesfor more information.

Renaming or moving categories

Please seeCommons:Rename a category.

For more appropriate categorization

Pages (including category pages) are categorized according to their subject, and not to their contents, because the contents are generally not a permanent feature of the category page; in particular, you can momentarily find inappropriate contents in a category page.

Example: Assume thatCategory:Spherescontains only pictures of crystal balls. You must not addCategory:Glassin the category page, according to the current contents, because you can have spheres made with a great variety of materials. Normally, any picture showing a glass object would be already categorized inCategory:Glass(or in a category of its substructure). So, if theCategory:Spheresis really crowded with crystal balls pictures, it would be a better idea to create a new category page, like Category:Glass spheres or Category:Crystal balls, categorized inCategory:SpheresandCategory:Glass.

Generally files should only be in the most specific category that exists for certain topic. For example files inCategory:Looking up the center of the Eiffel Towershould not also be inCategory:Paris(seeover-categorizationbelow).If you do not find a category that fits your purpose, you can create it — but carefully read the section aboutusing categoriesfirst.

This does not mean that an image only belongs in one category; it just means that images should not be inredundantor non-specific categories. For instance, an image of a Polar Bear being rescued from an iceberg by a helicopter should be inCategory:Ursus maritimus,Category:IcebergsandCategory:Rescue helicopters.It should not, however, be inCategory:Ursidae,Category:Sea iceorCategory:Aircraft.

Categorization tips

The categories (or galleries) you choose for your uploads should answer as many as possible of the following questions:

The above questions cover the main aspects of the image to be categorized. For some images it makes sense to use all, for other images only one or two are reasonable. In addition there are several other aspects of the images that can be used to categorize the image:

This last set is useful and important but should always be done in addition of the main set of criteria.

Categorization in Wikimedia Commons is more detailed and deep than categorization in Wikipedia projects. Compared to them, Commons has more categories for individual subjects – places, people, organizations, events, terms, etc. Almost every article on a Wikipedia can have a corresponding category on Commons. However, even if there exist more images of an ordinary person or incidental event, it is practical to group them into a special category and categorize that category instead of categorizing all similar images individually to an identical set of parent categories.

Find an appropriate category

To find appropriate categories for your uploads, you should navigate the category structure starting from a generic category. Narrow your search down to subcategories until you find the most specific category that fits the file you uploaded. You can navigate the category structure by following links to subcategories, or expanding the tree of subcategories by clicking on the little ▶ symbols on subcategory names. TheMajor categoriessection above provides a starting point, and theHow to categorize: guidance by topiccovers some topics more.

Over-categorization

for the inclusion criteria (the equivalent ofw:WP:OVERCAT) seeCommons:Category inclusion criteria

Don't place an item into a categoryandits parent. For example, a black and white photo of the Eiffel Tower should be placed inBlack and white photographs of the Eiffel Tower.It shouldnotbe placed in both that category and thePariscategory at the same time.
Shortcut

Over-categorization is placing a file, category or other page in several levels of the same branch in the category tree. The general rule isalways place an image in the most specific categories, and not in the levels above those.Exceptions to this rule are explained inthe section below.

Example: An image needing to be categorized shows a yellow circle. This image should be placed inCategory:Yellow circles.If it is also placed inCategory:Circles,it isover-categorized.We already know that it's a circle, because all yellow circles are circles. Therefore,Category:Circlesis redundant.Template:Uw-overcatcan be used to advise users of this.

This applies to most files: As mentioned under the adjacent illustration, files inCategory:Black and white photographs of the Eiffel Towershould not also be inCategory:Paris,files inCategory:Albert Einsteinshould not be inCategory:Physicists from Germanyand so on.

Why over-categorization is a problem

It's often assumed that the more categories an image is in, the easier it will be to find it. Another example: By that logic, every image showing a man should be inCategory:Men,because even if you know nothing more about the person you're looking for than that he is a man, you'll be able to find it. The result is that the top category fills up, making it necessary to go through hundreds, or in this case more likely thousands of images to find the one you want. You probably won't find what you're looking for, and what's more, those who are looking for a generic picture of a man to illustrate an article likeen:Manwill find that they've drowned out among the movie stars, scientists and politicians.

On lower levels, the problem becomes less acute, since the number of images will be smaller — they can still easily reach into the hundreds, though. But there is still a problem: Let's go back to Einstein. I know that he's a physicist, so I'll look in theCategory:Physicistscategory. I find an image of Einstein among the hundreds of images of other physicists, which I'm not too happy with, but it's the only one there. Since there was an image there, I assume that there are no more hidden elsewhere, rather than look further inCategory:Physicists from Germanyand thus findCategory:Albert Einsteinwhere there might be a better one. So over-categorization has led to two problems: The top category is cluttered, and users will stop looking for the most relevant category since they've reached one that has a relevant image.

Improper categorization of categories is a cause of over-categorization

Strange as it may sound, under-categorization can be a cause of over-categorization. When a category itself is not properly categorized, it can lead users to over-categorize files belonging in that category. An example of this:Category:Eivør Pálsdóttirwas categorized only inCategory:People by name.A user categorizing an image of her might then be tempted to also place the image inCategory:Female vocalists from the Faroe Islands.The correct solution is to place the image only inCategory:Eivør Pálsdóttirand to make that category a subcategory ofCategory:Female vocalists from the Faroe Islands.At that point, however, any images that were already placed into both categories become overcategorized and need to be manually removed from the parent category.

A related problem is erroneous categorization. Notting Hill is a district within the borough of Kensington and Chelsea in London. When it was created,Category:Notting Hillwas placed directly inCategory:Londoninstead of in theCategory:Royal Borough of Kensington and Chelseasubcategory, where it should have been placed. A user categorizing an image of Notting Hill might then be tempted to place it both inCategory:Notting Hilland inCategory:Royal Borough of Kensington and Chelsea.Instead, each image should be placed only in the most specific categories, and those categories should in turn be placed in their most specific categories.

When you encounter improperly categorized categories, please place them in the appropriate parent categories if you are able to do so. That will not only help avoid over-categorization, but it will also make it easier to move through the category tree.

Exception for images with more categorized subjects

A file that depicts only one relevant subject should not be over-categorized. Where a file depicts additional relevant subjects, and the additional subjects do not have their own subcategories, consideration can be given to temporarily categorizing the image in both the subcategory and the parent category.

For example, this situation might arise in the case of a photograph of three politicians, one of whom isAngela Merkel(who has her own Commons category), with two other politicians who do not yet have their own categories. While the image would undoubtedly be categorized inCategory:Angela Merkelor one of its subcategories, it would typically be considered to be over-categorization to also include it inCategory:Politicians of Germany.Users would, however, be unlikely to search for the two other politicians in the Merkel category. Ideally, we would create specific subcategories for the two other politicians (where warranted), or find other relevant subcategories (e.g.Category:Politicians of BavariaorCategory:Members of the FDP,etc.), that would enable us to avoid over-categorization. In some circumstances, however, we may need to temporarily categorize the image inCategory:Politicians of Germanywhere other appropriate subcategories do not yet exist.

Countries may be categorized as part of multiple overlapping categories. For example,Category:Indiais inCategory:Countries of South Asiaas well asCategory:Countries of Asia.

Also user categories are exempted of over-categorization as those are not visible to most viewers, and project users include them for many different purposes like sorting, stats, filling values for userboxes, etc.

How to categorize: guidance by topic

For some categories, there is special guidance on how best to sort content within that category. This guidance can be found in acategory schemeor aCommons projectfor your topic. There is also some categorizing information in this section and sometimes there is guidance at the top of the category's page, in the Categorynamespace.So, for instance, some guidance on categorizing content depicting people is at the top ofCategory:People,and some is in the sectionPeoplebelow.

Structures

Content depictingStructures,e.g.BuildingsandTunnels,can be classified like this:

Structure Category.First check if there is already a Category for this specific structure.

  • If yes: put it in there.
  • If no: If you have more than two pictures: create a new Category, named after the structure. For exampleCategory:Rheinbrücke Emmerich.Use the common name, not necessarily the English one.

Then you categorize the category (NOT each single picture!) under the following possibilities:

Afterwards, categorize the image by the way the structure is depicted, such as:

Also consider the part and the context visible:

People

Content depicting people should be put in categories which describe them, such asCategory:Economists from the United States.Start exploring atCategory:People.

Please seeCommons:Suggested category scheme for peoplefor details on how to name and organize these categories.

Landscapes, outdoor views

Content depicting a given subject from a common vantage point are grouped inViews of Subject from Viewpointcategories such asViews of Cathedral of Seville from the Giralda.Such categories should be subcategories of both the subject's category (Cathedral of Sevillein this example) and the viewpoint's category (Giraldain this example).

In this example, theViews of Cathedral of Seville from the Giraldacategory is not placed directly in the subject and viewpoint categories, but inViews of the Cathedral of SevilleandViews from Giralda.Such intermediate categories are often necessary to create structure and avoidover-categorization,particularly for views of a city from a vantage point located within the city. For example,Views of Rome from the Pincioneeds the intermediate categoryViews of Rometo avoid placing it directly inRome,which would constitute over-categorization.

Texts

Texts, such as scans of books, should normally have a category for each version of the scan and each edition of the text. Thus a book published in three separate editions would have a parent category for the book, three subcategories for each text, and further subcategories for the text as a jpeg, a DjVu, etc., assuming each version had actually been uploaded. (Categories would not be created for editions not held on Commons.) This is particularly important for files in formats other than DjVu and PDF, where the category is the only practical means of keeping the scans together; see eg.Category:The Chronicles of England, Scotland and Ireland, Holinshed, 1587which contains 2857 jpeg images of page scans.

GLAMs

For categorization issues related to mass content donations from GLAMs (Galleries, Libraries, Archives & Museums), please seeCommons:Guide to batch uploading#Categories.

Categorization workflow

Currently, a bot checks if newly uploaded files are categorized in topical categories and attempts to categorize files that are not. Before 17 June 2015,CategorizationBotwas responsible for this job. As of June 2019,SteinsplitterBotoccasionally checks for uncategorized files. The workflow is the following:

  1. User uploads a new file and adds categories (or not).
  2. A bot checks if the file is categorized.
  3. Users categorize files further (e.g. category diffusion below)

See also:User:CategorizationBot#Process,categorization statistics

Other, if manual, categorization workflows are possible:

  • Category filling: Use appropriate keywords in the search engine to find the files that should be in a given category, and put them there.
  • Category diffusing: Go toCategory:Categories requiring diffusion,select a crowded category, create appropriate subcategories if needed, and move the files to the subcategories. Gadgets like Cat-a-lot and HotCat can help.

Categories marked with "HIDDENCAT"

Shortcut

Many non-topical categories are marked with themagic word__HIDDENCAT__or{{Hiddencat}}on the category page. The advantage of using the template is that there will be an additional Infobox for the user stating that: 

"This category isnot shownon its member pages unless the appropriate user preference is set. "

An example of using__HIDDENCAT__isCategory:PD NASA.An example of using the template isCategory:Wildtunis/100WikiCommonsDays.

While categories are generally visible on every page, categories marked with__HIDDENCAT__or{{Hiddencat}}are only visible:

  • on the edit screen: at the end of the screen, below the edit box
  • on category pages:
    • on subcategories to the hidden category: in the normal location, but on a separate line with a smaller typeface and the label "Hidden categories."
    • on parent categories: in the same way as other categories
  • on file description pages and gallery pages: for logged-in users who have selected to "Show hidden categories" in theirappearance preferences.This is activated for all newly registered users.

This feature is generally used for template-based categories, such as license tag based categories. For example, placing{{PD-old-100}}on a file description page adds the file toCategory:Author died more than 100 years ago public domain images,which is marked with__HIDDENCAT__.

For more details, see thehelp section on hidden categoriesfor Mediawiki (the software that Commons uses).

Templates for categories

Some templates are designed for use on category pages - seeCategory:Category namespace templates.If the category is linked to a Wikidata entry, then you can use:

which displays a summary of the topic's information that is available on Wikidata, and also auto-adds birth/death/name/monument ID categories.

Some of the more commonly used ones areCategory:Category header templatessuch as:

Tools

Further information:Commons:Tools

See also

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