Wikipedia:Commons categories
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Attention: This page was interwikified from the source page Commons:Commons categories, which may have been changed since being copied here. Before using any information here, check the key paragraphs on that page. |
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This page in a nutshell: Categories help users navigate through Wikipedia and/or the Commons via multiple taxonomies. Categories are for defining characteristics, and should be specific, neutral, inclusive and follow certain conventions. |
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- See also: Wikipedia:Categories
This page is about the common Wikimedia projects' categories, beginning by the root category Category:Categories and the derived Commons:Category tree.
The category structure is the primary way to organize and find files on Wikimedia 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, and/or put on a gallery page which is categorized. Each category should itself be in more general categories, forming a hierarchical structure.
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[edit] Categories or galleries?
Note the "and/or" above. Some users are of the opinion that when an image is included in a gallery article, it is sufficient to categorize that article. Others believe that each individual image should be categorized too. The consensus on this issue, as determined by vote, is that both systems are equally valid and should be used concurrently. Do not remove categories just because an image is in a categorized gallery. It is hoped that in the future the software will be updated to merge the functionalities of galleries and categories into one. Automated tools for finding images must dig through categories and gallery articles.
[edit] Using categories
To add a page (be it an image, a gallery page, or a category page) to a category, add [[Category:Category Name]] to the end of the page. For information on how to find good categories for your uploads and galleries, read the section "Categorizing your uploads" below.
It is rarely necessary to create a new category—before doing so, make sure you are familiar with the existing category structure, and with the customs and policies of Commons. Please see if there exists a category scheme or a Commons project for your topic, and follow the conventions described there.
To create a new category, first use it on a page as described above. Then follow the red link to that category—you can now edit the category page 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.
- A short description text that explains what should be in the category. English is the preferred language for the description, other languages can be added.
- Interwiki links to categories or pages with the same topic in the Wikipedias.
Category names should always be in English—we still lack internationalization for category names, but this issue should be resolved with appropriate changes to the MediaWiki software (see bugzilla:5638). Creating intermingled category structures in different languages would only make things worse. Categories for life forms should use the scientific (Latin) name.
Category names that refer to objects or people should generally be in plural form: Category:Tools, Category:Artists, Category:Lakes, etc, as opposed to Category:History, Category:Weather, Category:Music.
For a general discussion of MediaWiki's category feature, see the Meta's manual page on categories.
[edit] Categorizing your uploads
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. The categories (or galleries) you choose for your uploads should answer at least one of the following questions:
- What? / Whom? what or whom does the file show? For instance, Category:Houses or Category:Jimbo Wales
- Where? where was the image taken? This is especially important for pictures of places, obviously. E.g. Category:Saxony
- When? this should provide some historical context, if relevant. An example would be Category:World War II
- How? this should give some information about the media type, like Category:Audio
- Who? if the artist is well known, like Category:Rembrandt, it makes sense to categorize by artist; you can also use the pages from the Creator namespace as templates to achieve this.
To find appropriate categories for your uploads, 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. The Category Structure section below provides a starting point. You can also try CommonSense, a tool that is designed to help with categorization based on keywords.
Generally, files should only be in the most specific category that exists for certain topic. For example files in Category:Paris should not also be in Category:France (see over-categorization below). If you do not find a category that fits your purpose, you can create it—but carefully read the section about using categories first.
This does not mean that an image only belongs in one category; it just means that images should not be in redundant or non-specific categories. For instance, an image of a polar bear being rescued from an iceberg by a helicopter should be in Category:Ursus maritimus, Category:Icebergs, Category:Helicopters, and Category:Search and Rescue. It should not, however, be in Category:Ursidae or Category:Aircraft.
Please provide as much details about your uploads as possible—see Template:Information for a suggestion on what to include. You must also provide license information for your uploads—see Commons:Licensing for details. See Commons:Project scope for information about what media are suitable for Commons.
[edit] Example
For example, if you are uploading a diagram showing the orbit of comets, you could add the following to the image description page:
{{W2c|Category:Diagrams}}
{{W2c|Category:Comets}}
This will make the diagram show up in the categories Diagrams, Comets.
[edit] Category structure
The category structure is (ideally) a multi-hierarchy with a single root category, Category:CommonsRoot. All categories (except CommonsRoot) should be contained in at least one other category, and there should be no cycles (i.e. a category should not contain itself, directly or indirectly). The category structure should reflect a hierarchy of concepts, from the most generic one down to the very specific.
The top-most categories (the ones contained directly in CommonsRoot) divide the category structure by the purpose of the contained categories:
- Category:Commons - this is for categories dealing with policies and maintenance tasks. Media files should be in that part of the category structure only if there's something wrong with them.
- Category:Image sources - this is for categorizing media files by where they come from (specific books, collections, etc.)
- Category:Copyright statuses - this is for categories that describe the license status of the media files they contain. Images can be put in one or more of these categories by using the appropriate license tag.
- Category:Media types - this is for categories describing the media type, like Audio, etc; Note that this type of categorization is usually omitted for images, since the vast majority of files on Commons are images of some sort.
- Category:Topics - this is the root of the topic hierarchy of Commons. All media files should be put into one or more categories in this part of the structure, to allow others to find them by topic.
- Category:User - this is for categories that contain Commons users, sorted by things like the language they speak. This also contains the :Category:User galleries, which is for user specific (i.e. non-topic) galleries.
[edit] Over-categorization
Over-categorization is what happens when an image is placed in several categories within the same tree. The general rule is always place an image in the most specific categories, and not in the levels above those. An example:
We'll assume that yellow spheres are spheres with a yellow color. We can think about Category:Yellow spheres and Category:Spheres. The picture to be categorized shows yellow marbles. We categorize the file in Category:Yellow spheres. Now, if we also categorize the image file in Category:Spheres, this is over-categorization: because we already know that the yellow marbles are spheres. This applies to most images: As mentioned above files in Category:Paris should not also be in Category:France, files in Category:Albert Einstein should not be in Category:Physicists from Germany and so on.
[edit] Why is over-categorization 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 in Category: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 like Man will 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 there. I find an image among the hundreds in the category, 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 in Category:Physicists from Germany and thus find Category:Albert Einstein where 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.
[edit] Improper categorization of categories is a cause of over-categorization
Strange as it may sound, under-categorization can actually be a cause of over-categorization. This happens when a category is not properly categorized, leading users to over-categorize an image to get it into the relevant categories. An example of this: Category:Eivør Pálsdóttir was categorized only in Category:People by alphabet. So if I add an image of her, and know who she is, I would also place the image in Category:People of the Faroe Islands and Category:Vocalists. This is over-categorizing, I've caused clutter in the top categories by adding images directly to them.
A related problem is erroneous categorization: Category:Notting Hill was for more than a month placed in :Category:London. When adding an image, it would be very tempting to add that image to Category:Kensington and Chelsea, which is where you'll find Notting Hill. Instead, each image should be placed only in the most specific categories, and those categories should in turn be placed in its most specific categories.
When you encounter this, please categorize the categories properly if you are able to do so. That will not only help avoid over-categorization, but also make it easier to move through the category tree.
