Categorization

Categorization is the practice of placing pages (articles, files, templates, portals, drafts, etc.) into categories to group related content and aid navigation and maintenance. Categories should reflect what a page is, rather than everything it mentions.

Purpose

Organize content into coherent topic areas.
Provide readers and editors with navigational aid beyond search.
Support maintenance through tracking and hidden categories.
Complement, not replace, lists, portals, and Wikidata.

Principles

Verifiability and relevance: categorize based on reliably sourced, defining characteristics.
Non-diffusing vs diffusing: know whether subcategories are meant to include all members of the parent or only a subset.
Minimal necessary: avoid overcategorization and category creep.
Neutrality: categories are not used to promote viewpoints.
Consistency: follow established conventions within category trees.

Category structure

Hierarchical: categories form trees via parent–child relationships.
Top-level: broad categories (e.g., ) branch into specific subcategories.
Subcategories: place pages in the most specific applicable category.
Overlap: acceptable when subjects legitimately belong to multiple areas; avoid redundant parallel placement when a subcategory already implies the parent (diffusing).
Non-diffusing: some parents expect direct members even if subcategorized (e.g., may be non-diffusing).

Naming conventions

Use plural nouns for topical categories: Category:Astronomers.
Use singular for set types when standard: Category:Physics (field), Category:Mathematics.
Disambiguate with parentheses if needed: Category:Mercury (planet) vs Category:Mercury (element).
Biographies: follow established patterns (e.g., Category:1975 births, Category:Living people, nationality + occupation).
Avoid POV or contentious labels without consensus and sources.

Placement rules

Place categories at the bottom of the page:

  [[Category:Physics]]
  [[Category:Quantum mechanics]]

Order: most wikis do not enforce strict ordering; keep logical and readable.
Specificity: prefer the most specific valid category; do not also add the parent if the tree is diffusing.
Non-diffusing exceptions: add both the specific subcategory and the parent when the parent is marked non-diffusing.
Biographies: add chronological (births/deaths), living people status, nationality, occupation, and notable attributes where sourced.
Files: categorize by subject, format, license, and source when appropriate.
Templates and modules: place maintenance categories inside <noinclude></noinclude> on the /doc subpage to avoid categorizing articles.

Hidden and tracking categories

Hidden categories do not display to readers by default; they assist maintenance.

__HIDDENCAT__

Tracking categories collect pages with specific issues (e.g., pages using deprecated parameters).
Add tracking categories programmatically via templates or modules; document them on the template’s /doc page.

Lists, portals, and categories

Categories are navigational groupings; lists provide curated selections with context.
Portals offer topic overviews and entry points; use categories to underpin portal content.
Do not replace comprehensive list articles with categories; they serve different purposes.

Wikidata and categories

Wikidata provides structured data; categories provide human-readable groupings.
Do not auto-categorize articles solely based on Wikidata claims without local consensus.
Use Wikidata to help maintain category consistency (e.g., via bots), with review.

Categories for living people

Exercise caution; follow Wikipedia:Biographies of living persons.
Avoid contentious or unsourced categories (e.g., alleged crimes, medical conditions) without high-quality sources and consensus.
Prefer neutral, verifiable descriptors.

Maintenance categories

Use for cleanup, backlog tracking, and process organization (e.g., Category:Articles needing citations).
Hide such categories when placed on articles:

[[Category:Articles with short description|*]] <!-- hidden via site config; readers won’t see it -->

Place directly on maintenance templates so they add categories when used.

Template interaction

Templates often add categories automatically based on parameters.
Prevent categorizing the template page itself:

  <noinclude>[[Category:Documentation pages]]</noinclude>

For conditional categorization, document logic clearly and test with Special:ExpandTemplates.

Creating a category

Create the category page with a short, neutral description and parent links:

  {{Category description|A category for articles about quantum field theory.}}
  [[Category:Quantum mechanics]]
  [[Category:Theoretical physics]]

Add {{DEFAULTSORT}} where appropriate to control sort keys for members.
Consider adding a scope note and inclusion criteria.

Sort keys

Control alphabetical ordering within a category using {{DEFAULTSORT:Last, First}} or per-entry sort keys:

[[Category:Astronomers|Einstein, Albert]]

For biographies, use Last, First unless local conventions differ.
For titles starting with articles (The/A/An), adjust sort keys to ignore articles.

Non-mainspace pages

Project pages, help pages, and templates may have their own organizational categories.
Keep separation between content categories (articles) and administrative categories (maintenance, project).

Common mistakes

Overcategorizing (too many categories, marginal relevance).
Using categories for temporary or trivial attributes.
Failing to respect diffusing vs non-diffusing rules.
POV or contentious labeling without sources or consensus.
Categorizing via templates without placing categories inside for the template page.

Best practices

Categorize based on defining characteristics supported by sources.
Prefer specific subcategories; avoid redundant parent placement when diffusing.
Document category scope and inclusion criteria on the category page.
Use sort keys consistently; add Template:DEFAULTSORT on articles where needed.
Review categories during major edits; keep trees tidy and logical.
Leverage hidden tracking categories for maintenance rather than public topical categories.

Tools

Special:Categories — browse all categories.
Special:CategoryTree — visualize category hierarchies.
Special:WhatLinksHere/Category:Name — find pages in a category.
Special:PrefixIndex/Category: — list categories by prefix.
Special:Search — locate candidate pages for categorization.
Special:ExpandTemplates — test template-driven categorization.

Examples

Article:

  [[Category:American physicists]]
  [[Category:Quantum field theorists]]
  {{DEFAULTSORT:Einstein, Albert}}

Template doc:

  <noinclude>
  [[Category:Template documentation pages]]
  </noinclude>

Category page:

  {{Category description|Articles related to exclamation marks and punctuation.}}
  [[Category:Punctuation]]

Wikipedia:Categorization