View source for Wikipedia:WikiProject Aviation/Style guide/Categories

== Categories ==

=== Overview ===
:''An alternate to this scheme is currently drafted at [[Wikipedia:WikiProject Aircraft/Categories/Proposed update]].''

The category scheme originates in one root category—[[:Category:Aviation]]—and can be thought of as a [[tree structure]].  A guide to the top-level sub-categories of this category is presented below; for brevity, a number of categories that are rarely used or lie outside the scope of this project have been omitted. 

; [[:Category:Aviation]] : Root category for matters related to aviation. This category should be empty of articles,
:; [[:Category:Aerobatics]] : Root category for all topics related to aerobatics. 
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{{seealso|Wikipedia:WikiProject Aircraft/Categories}}

=== General principles ===

==== Naming ====

:''For naming conventions related to categories, see the [[#Category names|section on naming conventions]] above.''

==== Most specific categories ====

In general, articles and categories should be placed in the ''most specific'' applicable categories, and should not be placed directly in a "parent" category if they are already present in one of its sub-categories.  In other words, if an article is placed in [[:Category:United States airliners 1940-1949]], there is no need to place it in [[:Category:United States civil aircraft 1940-1949]] or [[:Category:Aircraft manufactured by the United States]] as well.

Note, however, that this applies only to ''direct'' placement into a "parent" category; it is normal for a category to have multiple ''indirect'' paths up to some other category higher in the tree.  For example, [[:Category:United States military transport aircraft 1940-1949]] is both a sub-category of [[:Category:Military transport aircraft 1940-1949]] (which is a sub-category of [[:Category:Military aircraft 1940-1949]]) and a sub-category of [[:Category:United States military aircraft 1940-1949]] (which is ''also'' a sub-category [[:Category:Military aircraft 1940-1949]]); thus, there are two distinct paths from [[:Category:United States military transport aircraft 1940-1949]] up to [[:Category:Military aircraft 1940-1949]].  This is especially common when dealing with [[#Intersection categories|intersection categories]].

==== Nested categories ====
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==== Intersection categories ====
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=== Aircraft ===
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=== Airlines ===
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=== Airports ===
Airport articles should include the most specific category possible based on location. Each [[country]] has its own airport category, which can be found at [[:Category: Airports by country]] (also available grouped by [[continent]] at [[:Category: Airports by continent]]). For example, [[Copenhagen Airport]] in Denmark includes '''[[:Category: Airports in Denmark]]'''.

Some larger countries have sub-categories for first level [[administrative division]]s, such as [[state]] or [[province]]. These can be found under the country's airport category and should be used where available. For example, [[Québec City Jean Lesage International Airport]] in the [[Canadian province]] of Quebec includes '''[[:Category: Airports in Quebec]]''', a sub-category of [[:Category: Airports in Canada]] (which is not added to the article).

Airport articles often include a location category for an administrative division below that of the airport category. For example, [[Nice Côte d'Azur Airport]] in Nice, France, includes both [[:Category: Airports in France]] and '''[[:Category: Nice]]'''.

Besides the location related categories, some airport articles may include other categories, such as those listed at [[:Category: Airports by type]]. For example, [[Independence State Airport]] in the [[U.S. state]] of Oregon includes '''[[:Category: Residential airparks]]''' in addition to [[:Category: Airports in Oregon]] and [[:Category: Polk County, Oregon]].