Wikipedia data structure
Subject namespaces Talk namespaces
0 (Main/Article) Talk 1
2 User User talk 3
4 Wikipedia Wikipedia talk 5
6 File File talk 7
8 MediaWiki MediaWiki talk 9
10 Template Template talk 11
12 Help Help talk 13
14 Category Category talk 15
100 Portal Portal talk 101
118 Draft Draft talk 119
710 TimedText TimedText talk 711
828 Module Module talk 829
108 Book Book talk 109
2300 Gadget Gadget talk 2301
2302 Gadget definition Gadget definition talk 2303
-1 Special
-2 Media

Categories are intended to group together pages on similar subjects. They are implemented by a MediaWiki feature that adds any page with a text like [[Category:XYZ]] in its wikimarkup to the automated listing that is the category with name XYZ. Categories help readers to find, and navigate around, a subject area, to see pages sorted by title, and to thus find article relationships.

Categories are normally found at the bottom of an article page. Clicking a category name brings up a category page listing the articles (or other pages) that have been added to that particular category. There may also be a section listing the subcategories of that category. The subcategorization feature makes it possible to organize categories into tree-like structures to aid navigation.

The term category does refer to both the title of a category page—the category pagename—and the category itself. Keeping this in mind while reading about categorization, plus learning a category page layout is a worthwhile investment in research techniques. (See also the search box parameter "incategory".) The layout of a category page is mostly text, but see about displaying category trees below.

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