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This page will serve as a central operating point for the different categorization projects.

Useful links

Guidelines for assignment

If this section stabilizes, it should probably be moved into the User's Guide. -- Beland 08:06, 13 Jun 2004 (UTC)
Maybe with a major rewrite. It is all but useless right now, giving no basic information on How to create categories/subcategories - Marshman 21:57, 5 Jul 2004 (UTC)

Categorization, as explained below, creates a tree or hierarchy of articles. When adding an article to a category, or creating categories, one should be careful to use the correct categories and subcategories. Horizontal categorization, directly below, refers to placing an article in the correct category, vertical categorization refers to placing an article in the correct subcategory.

When assigning an article into categories, try to be thorough in a "horizontal" sense. The topic may be associated with a geographic area, a historical period, an academic subfield, a certain type of thing (like a food or an ornament), and/or a special interest topic (like Roman Empire or LBGT). You might need to poke around the category hierarchy a bit to find the right place. Try searching for articles similar to the article you are categorizing to get ideas or to find the most appropriate place. (for instance, 1990 is in 'Category:Time periods' rather than 'Category:Places')

In the "vertical" dimension, you should probably be more frugal. A good general rule is that articles should be placed in the most specific categories they reasonably fit in. For example, Queen Elizabeth should not be listed directly under People, but Queens of England might be a good place for her. We know that all Queens of England qualify as Famous Britons and as Royalty, and all of those folks qualify as People. But sometimes there's a good reason to assign an article to two categories, one of which is a direct or indirect subcategory of another. For a well-argued case study, see John Lennon. (1990 is in 'Category:Years', a subcategory of 'Category:Time periods)

Whatever categories you add, make sure they do not implicitly violate the neutral point of view policy. If the nature of something is in dispute (like whether or not it's fictional or scientific or whatever), you may want to avoid labelling it or mark the categorization as disputed. Most categorizations are pretty straightforward, though.

Making trees

When a given category gets too crowded, consider making subcategories. Group similar articles together in a meaningful way that will hopefully be easy for readers to navigate later.

A set of related categories often forms a hierarchy or a nexus. This can take several different forms, all of which are welcome and encouraged:

  • Hybrid forms. For example, Category:Art is both part of a the taxonomy of Category:Acadaemia and a cross-reference point for lots of things that have little in common except that they have something to do with art.

Category membership and creation

When writing the description for a category, give it a parent category. In fact, you should try to give it at least two parent categories. For example, Category:British writers should be in both Category:Writers by nationality and Category:British people. A few categories do only merely subdivide their parent category, but unless the parent category has many potential articles under it, or many potential subdivisions, if you can't think of a second parent category, it might be a better idea to fold your smaller category into the parent.

Misplaced Pages namespace

Categories relating to the Misplaced Pages namespace should be added only to the talk page of articles. For example, tags suggesting the article is unfinished, or is listed on VfD would be placed on the talk page as they are relevant to editors, not an aid to browsing in the way ordinary categories are. Please use {{wpcat}} on the Category description page to show that it is a Misplaced Pages-namespace category.

General naming conventions

  • Avoid abbreviations. Example: "World War II equipment", not "WW2 equipment".
  • Don't hard-code the category structure into names. Example: "Monarchs", not "People - Monarchs".
  • Topical category names should be singular. Examples: "Biology", "Law".
  • Standard naming conventions apply; in particular, do not capitalise regular nouns.

Special conventions for lists

  • Category names for lists of items should be plural. Examples: "sports", "writers".
  • In instances where "List of Quuxen" is a simple alphabetical enumeration with no other information on it (unlike List of Twilight Zone episodes, for instance), it could be replaced with "Category:Quuxen".
  • Comprehensive lists, e.g. "List of all municipalities of Quuxen", annotated lists, and selective lists, e.g. "List of Quuxens that were Bazzed", should not be replaced with categories.
  • Names such Category:Lists of Quuexens should be used only for pages with lists, such "List of Quuexens that were sdfdd"
  • See: Category:Lists, Category:Lists that should be categories.

Note that there are a growing number of instances where both the singular category (listing topics relating to) and plural category (listing instances of) exist, for example, Category:Opera and Category:Operas. Be careful to choose the right one when categorizing articles.

Categories requirements and usage

User browsing

Categories (along with other features, like cross-references) should help users find the information they are looking for as quickly as possible, even if they don't know that it exists or what it's called.

Links to categories

You can create a link to a category page without adding the page to that category by using a colon before the word, Category. Example: ] appears as Category:Automotive Technologies.

Category sorting

Contrary to some expectations, text after a pipe ("|") in a category link is not used in place of the category text. Rather, this text is used as the sort key on the category page itself. However, again contrary to expectations, that sort text is not displayed.

For example, the Category:U.S._Interstate_Highway_system uses this property to sort secondary interstates by their primary. That is, the category link in the article for Interstate 190 is ]. This causes "Interstate 190" to be listed right after "Interstate 90" and right before "Interstate 290" under the heading "9" in the category page.

This feature is very useful:

It can even improve categories lists where every article begins with the same word (example: Category:Mazda).

Using this method to sort category entries is sometimes informally referred to as the pipe trick.

Category extraction

An advantage of categorization is that it allows extraction of large portions of Misplaced Pages. For instance, if years and dates were as below (leftmost items are regular articles, the rest are categories), extracting, say, a timeline for the 21st century would be trivial. 

2004 -> Years in the 21st century -> Years -
                                            \
                                             --> Time periods
                                            /
30 March -----> Days in March ----> Days ---
Please expand this explanation. I see no way from this to "extract a timeline for the 21st century" just a way to create a list of, say, years in the 21st century or days in March. So where is the whoopie in that? - Marshman 17:32, 5 Jun 2004 (UTC)
Where this becomes slightly more interesting is when you have articles on historical events (e.g. Pearl Harbor, John F. Kennedy's Birth, the Great Northeast Blackout, etc.) put in the appropriate time-related category. But the ability to do completely automated extraction depends on how structured the category relationships are. You'd ideally like to be able to specify that the article is about an "event that occurred during" the category or "is a part of" or "is a member of" (say, for geographical or political relationships). So far we can only specify generic parent-child and "is related to" assignments; any other semantics must be inferred. -- Beland 09:32, 13 Jun 2004 (UTC)

Current projects

See: Misplaced Pages:Categorization projects (current)

Rendering issues

  1. There are nasty display bugs on category pages which have articles categorized in them, but for which the actual category page has not yet been created by editing. silsor 02:35, Jun 15, 2004 (UTC)
  2. There appears to be a bug - if you list more than one category, each on a line by itself, you get extra and unwanted blank lines rendered at the end of the article. This doesn't seem to happen with inter-language links. -- Beland 10:12, 5 Jun 2004 (UTC)
  3. The table that is rendered conflicts with floating tables, see for example: Annibale_de_Gasparis. This could be fixed simply by adding this to the beginning of the category template:
<br style="clear:both" />
  1. Under some circumstances the descriptive text for the Category appears under the table of articles --Phil | Talk 09:20, Jun 16, 2004 (UTC)


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