User:DexDor/Namespaces and categories

This is an essay on Wikipedia categorization.

It contains the advice or opinions of one or more Wikipedia contributors. This page is not an encyclopedia article, nor is it one of Wikipedia's policies or guidelines, as it has not been thoroughly vetted by the community. Some essays represent widespread norms; others only represent minority viewpoints.

Shortcut

User:DexDor/NSCat

Every Wikipedia page (e.g. an article, a talk page or even a redirect) is in a single namespace. Many/most Wikipedia pages are also in one or more categories. This essay contains the results of an analysis of how these 2 schemes interact - i.e. how pages in each namespace fit into the category structure.

The essay also contains some information about detecting anomalies in the categorization and correcting them.^[1]

Namespace-category matrix

Note: The information in this matrix should not be used directly to support an argument about whether or not a particular page should be in a parent category. However, this matrix may indicate where the applicable policy/guideline can be found.

The analysis was carried out in 2014-2015 using category intersection tools. Some aspects of the analysis are currently incomplete and may not incorporate later changes to the categorization structure.

Explanation of matrix

The matrix is designed so that each page in the English Wikipedia satisfies the criteria for one (and only one) of the rows.^[2] Which row a page matches is determined primarily by which namespace the page is in; for some namespaces other criteria are also considered -

Some rows are only applicable to disambiguation pages (i.e. pages that are under Category:Disambiguation pages) or non-disambiguation pages. The column headed "D?" indicates whether each row includes disambiguation pages - "Y" means only dab pages, "N" means excluding dab pages and "-" means either.

Some rows are only applicable to hard redirects or to pages that are not hard redirects. The column headed "R?" indicates whether each row includes hard redirects. "Y" means only hard redirects, "N" means excluding hard redirects and "-" means either.

Some rows are only applicable to subpages. The column headed "S?" indicates whether each row includes subpages. "Y" means only subpages, "N" means excluding subpages and "-" means either. Subpages are not allowed in some namespaces.

Some rows are only applicable to pages that are, or are not, in certain categories.

Having identified which row of the matrix a page belongs to the coloured cells on that row then indicate which high-level categories the page should/may be in (green cells) and should not be in (pink cells). The matrix can also be used in the opposite way; for a particular high-level category it is possible to go down the corresponding column to see what types of pages are expected to be in that category. Amber cells indicate where there is currently uncertainty about whether or not that is a valid combination. A more detailed key to the colours is provided below the matrix.

Matrix

Key

The cells in the matrix are of the following types:

		Column headings.
		Row definition. Where a greek letter is shown this is for use in sortkeys.
	never	This is not a possible combination. I.e. any page that satisfies the inclusion criteria for that row could not satisfy the inclusion criteria for that column (and vice versa).
	no	An existing WP guideline says (or implies) that there should be no pages at this intersection. If there is a database report that lists pages at this intersection then that also indicates that there should be no pages at the intersection. Many/most of these cells have a link to an explanation of why there should be no pages at that namespace/category combination.
	none	Few/no pages are found at this intersection (generally using category intersection to depth 6) - and any such pages are probably mis-categorized. It thus appears that either this is not a valid intersection for pages to occupy and/or it is not used by convention.
	some / yes / all	This is, or may be, a valid namespace-category combination.
	all	By definition every page in that row must be in that parent category (but not necessarily vice versa).
	tbd	To be decided - e.g. further investigation or discussion needed to resolve whether or not this is a valid combination.
	tbd	To be decided - uncertainties about the correct categorization of categories need to be resolved first.

Top-level category structure

The diagram below shows the top levels of the category structure. The two-letter codes are those used in the matrix above.

           Contents
             |
   -----------------------------------------------------------------------...
  |                              |          |        |           |
Wikipedia administration     Articles    Help    Portals    Wikipedia books
  |                             (CA)      (CH)      (CP)         (CB)
  |
   -----------------------------------------------------------------------------------------------...
      |                 |         |            |         |            |              |
 Wikipedia templates    |   Wikipedia essays   |   WikiProjects   Wikipedians   Wikipedia files
     (CT)               |        (CE)          |       (CW)          (CU)            (CF)
                        |                      |
            Wikipedia redirecting        Wikipedia disambiguation
                        |                      |
            Wikipedia redirects          Disambiguation pages
                       (CR)                   (CD)

Maintenance of the matrix

Template used to generate the matrix

The namespace-category matrix shown above is generated using a template (User:DexDor/Cmtp). The advantage of using a template rather than placing the details directly in this page is that parameters can be used to control how the template is displayed - thus, the template can generate both the compact format shown above and a longer more detailed format used during development of the matrix. There is also a similar template which expands the CA column into lower level article categories. Other templates are also used by the 2 top templates to avoid unnecessary repetition of code.

Note: watchlisting this page will not show changes to the matrix - for that it's necessary to watchlist the template.

Category intersection tools

The following table summarises facilities that some/all current category intersection tools do not have that would be useful to help identify whether there are any pages at particular positions in the grid.

Facility	http://tools.wmflabs.org/quick-intersection	http://tools.wmflabs.org/catscan2/catscan2.php
Option to select only subpages	No	TBD
Option to exclude subpages	No	TBD
Category intersection with no cat - e.g. pages in Book namespace that are not in Category:Books	TBD	TBD
Not follow redirect when click on link (it is confusing and it wastes time loading what can be a big page when it's actually the redirect page that is of interest)	TBD	TBD

Finding and fixing anomalies

Record

Record of some clearing up (to track cells that need to be checked):

Intersection   Depth  User     Date      Before   After
 14AinCU        6     DexDor   8/3/2015     9        0
   5inCA        6     DexDor  14/3/2015    36       23 (mostly AFC drafts)

Tips

To run a category intersection query: Press shift key click (normally in a way that causes a new window/tab to be opened) on a query link in the matrix, alter the depth if necessary (to minimise processing needed and to avoid unnecessary difficulty in resolving don't use too high a value), click on "Do it!".

Tips for investigating pages at unexpected namespace-category intersections:

Go to Special:Preferences#mw-prefsection-rendering and turn on "Show hidden categories".

When pages are examined in most cases it's easy to find a [[Category:Foo]] or [[W:Category:Foo]] tag that's causing the categorization. Sometimes it's not so obvious - usually because of a template - e.g. Template:Film date was putting pages (e.g. User talk:Musfar23) in a category (since deleted) which was under Category:Articles. In these cases Special:ExpandTemplates may help to identify where in the page the category is appearing - and hence which template is adding the category (and it's worth looking in the category for the template page).

Tips for fixing such pages:

To avoid a template categorizing pages in certain namespaces see Wikipedia_talk:Database_reports/Polluted_categories#Request_for_assistance_updating_templates_that_autocategorize.

If the page found is a talk page and has no corresponding non-talk page and has no inlinks (apart from any maintenance pages) and is not transcluded[6] (how tell?) and is not needed for licencing (??? see this) then propose the page for deletion by WP:CSD#G8.

Types of problems found

The table below shows examples of things found when checking pages at namespace-category intersections - and how to fix them. This table does not include problems caused by the category structure being incorrect (e.g. a category for Wikipedia administration being placed under Category:Articles).

Cause	Why it's a problem	Fix
Disambiguation page is in an article category (0DinCA)
A disambiguation page contains incorrect category tag.	Clutters up parent category, blurs distinction between an article and a dab page.	Remove the incorrect category tag(s) (e.g. [7]).
Page in User namespace in article category (2inCA)
A userpage (e.g. a WP:FAKEARTICLE has been placed in a category (e.g. in Category:Musicians).	Clutters up the article category	1. Comment out the category tag(s) (per WP:USERNOCAT). 2. Consider whether the page should be blanked or deleted (e.g. by CSD#U5).
Page in Wikipedia namespace in article category (4inCA)
An article is in the wrong namespace (having either been created in the wrong namespace or moved to the wrong namespace).	Causes confusion	1. Check if there's already an article in the correct namespace - if so see row below. 2. Consider deleting the page (e.g. M F D). 3. If not then move the article ([8][9]). Optionally delete the redirect that has been left in Wikipedia namespace (e.g. ??).
An article is duplicated in the wrong namespace.	Duplicate article, causes confusion	Delete the page in the wrong namespace (e.g. MFD/CSD) or turn it into a (cross-namespace) redirect (e.g. ??) (and then RFD/CSD the redirect?).
A Wikipedia admin page is incorrectly categorized as an article.	Clutters up parent category	Remove incorrect category tag (e.g. [10][11]). If necessary, add a more appropriate category tag (e.g. [12]).
A bot-generated list of pages refers to a category, but not using ":".^[10]	Clutters up parent category, confuses users of list	1. Insert ":" (e.g. [13]). 2. Optionally, see if the bot is still making this error (i.e. has made this error recently) and if so contact the bot operator (e.g. ??).
A Wikipedia admin page (e.g. a discussion page such as AFD) refers to a category, but without the extra ":".	Clutters up parent category, confuses text/discussion^[11]	Insert ":" (e.g. [14][15][16]). Optionally put the category tag inside markup (e.g. "<small>[[:Category:Foobar]]</small>") as a bit of an indication that this is not how the text appeared earlier (e.g. [17]).
A template is transcluded into a Wikipedia admin page and the template puts the page in an article category. Typically this occurs where a wikiproject has a list of templates relevant to the wikiproject that shows what the template looks like.	Clutters up parent category	1. Note what articles are in the category. 2. Decide whether it's appropriate for the template to categorize the page (generally it's not appropriate for a template to place a page in an article category). 3. Identify which template is causing the categorization. 4. Edit the template to remove the category tag (e.g. [18][19][20][21][22]) or to only categorize pages in mainspace (e.g. [23]). 5. Check whether or not articles (that were) in the category need the category tag to be added (e.g. [24]).
A category for Wikipedia administration that contains pages in the Wikipedia namespace (e.g. a Wikiproject category) has been placed in an article category.	Clutters up parent category, prevents other checks	Remove the incorrect category tag (e.g. [25][26]). Optionally replace by a more appropriate category tag (e.g. ??).
Template page is in an article category (10inCA)
A template page contains incorrect category tag.	Clutters up parent category, may hide fact that template is not appropriately categorized under Category:Wikipedia templates.	Remove the incorrect category tag (e.g. [27][28]).
Talk page in article category (1inCA, 3inCA, 5inCA ...)
A comment on the talk page refers to a category, but without the extra ":".	Clutters up category, confuses discussion	Insert ":" (e.g. ??).
A category for Wikipedia administration that contains talk pages (e.g. a Wikiproject category) has been placed in an article category.	Clutters up category, prevents other checks	Remove the incorrect category tag (e.g. ??, similar to above).

Other: An article is transcluded into a page in a different namespace (e.g. a user page).

References

^ Some examples of corrections made: [1][2][3].
^ Note: Currently there may be a small number of pages that don't fit any row of this matrix.
^ E.g. there are articles below Category:Wikipedia articles incorporating a Leigh Rayment's Peerage Pages template that is below Category:Wikipedia sources.
^ Pages that are soft redirects (e.g. see Category:Redirects to Wiktionary) are at this intersection. Also (temporarily) hard redirects that are at RFD. Pages that have been (incorrectly) placed under a redirected category are at this intersection - see Category:Wikipedia non-empty soft redirected categories.
^ As of March 2015 there's also lots of pages at this intersection because of redirects in Category:WikiProject Artemis Fowl and Category:Redirects from books (which is, possibly incorrectly, categorized under a wikiproject).
^ Pages get here for a variety of reasons - (1) because a template (example) is created in Draft namespace and has been placed in a templates category, (2) a page in Draft namespace (example) uses a template in such a way that it puts the page in a tracking category (e.g. Category:WikiProject banners with formatting errors or Category:Geobox usage tracking for region type) that is under Category:Templates (which itself is dubious), (3) a page in Draft namespace (example) is in Category:Template test cases that is under Category:Templates.
^ As of November 2015: 108RinCR indicates that there are 255 hard redirects that are in Book namespace in Category:Wikipedia redirects. Wikipedia:Database reports/Page count by namespace shows there are 764 (presumably hard) redirects in Book namespace.
^ As of November 2015: 100RinCR indicates that there are 1587 hard redirects that are in Portal namespace in Category:Wikipedia redirects. Wikipedia:Database reports/Page count by namespace shows there are 11227 (presumably hard) redirects in Portal namespace.
^ E.g. "Please ... add [redirect] templates ... when you create a redirect".
^ Note: Lists of pages generated by users can also have this error - e.g. [4]
^ E.g. "It is also important to add your articles to the and the prospective subcategories such as." prior to this edit[5].

Cite error: There are <ref group=lower-alpha> tags or {{efn}} templates on this page, but the references will not show without a {{reflist|group=lower-alpha}} template or {{notelist}} template (see the help page).

[1] Some examples of corrections made: [1][2][3].

[2] Note: Currently there may be a small number of pages that don't fit any row of this matrix.

[4] E.g. there are articles below Category:Wikipedia articles incorporating a Leigh Rayment's Peerage Pages template that is below Category:Wikipedia sources.

[5] Pages that are soft redirects (e.g. see Category:Redirects to Wiktionary) are at this intersection. Also (temporarily) hard redirects that are at RFD. Pages that have been (incorrectly) placed under a redirected category are at this intersection - see Category:Wikipedia non-empty soft redirected categories.

[6] As of March 2015 there's also lots of pages at this intersection because of redirects in Category:WikiProject Artemis Fowl and Category:Redirects from books (which is, possibly incorrectly, categorized under a wikiproject).

[7] Pages get here for a variety of reasons - (1) because a template (example) is created in Draft namespace and has been placed in a templates category, (2) a page in Draft namespace (example) uses a template in such a way that it puts the page in a tracking category (e.g. Category:WikiProject banners with formatting errors or Category:Geobox usage tracking for region type) that is under Category:Templates (which itself is dubious), (3) a page in Draft namespace (example) is in Category:Template test cases that is under Category:Templates.

[8] As of November 2015: 108RinCR indicates that there are 255 hard redirects that are in Book namespace in Category:Wikipedia redirects. Wikipedia:Database reports/Page count by namespace shows there are 764 (presumably hard) redirects in Book namespace.

[9] As of November 2015: 100RinCR indicates that there are 1587 hard redirects that are in Portal namespace in Category:Wikipedia redirects. Wikipedia:Database reports/Page count by namespace shows there are 11227 (presumably hard) redirects in Portal namespace.

[10] E.g. "Please ... add [redirect] templates ... when you create a redirect".

[11] Note: Lists of pages generated by users can also have this error - e.g. [4]

[12] E.g. "It is also important to add your articles to the and the prospective subcategories such as." prior to this edit[5].

[1]

[2]

[a]

[3]

[4]

[5]

[6]

[7]

[8]

[9]

[10]

[11]