User:Reinhard Müller/Category Sortkeys

General rule: Every category has a “natural” way of dividing it into subcategories:

• For meta categories, it's always the “by”-criterion. Example: natural subcategories of Mountains by country are Mountains of France, Mountains of Italy, and so on.
• For class categories and intersection categories, it's either a consistent set of subclasses or the instances of the class. Examples: natural subcategories of Landforms of Finland are Mountains of Finland and Cliffs of Finland, while natural subcategories of Mountains of Finland are the actual mountains.
• For object categories, it's the different topics relevant for this object. Example: natural subcategories of Germany are Culture of Germany, Geography of Germany, History of Germany, and so on.

The natural subcategories are always sorted with the @/A-Z keys. All other subcategories should go into a special sortkey or into a meta-subcategory.

Key	Usage	Abstract Categories	Class Categories	Meta Categories	Intersection Categories	Object Categories	Reasoning
	Example parent categories:	Geography	Mountains	Mountains by country	Mountains of France	Mont Blanc
criterium	Subordinate meta-categories where the content of this category is devided according to a specific criterium	Geography by country	Mountains by country	Mountains by country by height	Mountains of France by region		Sorted at the very beginning.
!criterium	Meta-meta-categories where subordinate meta categories are sorted by the same criterium			Mountains by season by country			Sorted just below the previous block.
#presentation	Subcategories concerning the way the topic is presented, like “Views of X”, “Videos of X”, “X in art”...	Geography in art	Videos of mountains	Views of mountains by country	Panoramics of mountains in France	Maps of Mont Blanc	A way of categorizing which is totally different from and additional to the normal category hierarchy, thus before the other special sortkeys.
$award	Subcategories with Highlighted content	Valued images of Geography	Featured pictures of mountains	Quality images of mountains by country	Valued images of mountains of France	Featured pictures of Mont Blanc	These media are very valued by the community, thus the $.
%part	Subcategories which cover only a defined part of the objects, like doors of houses, leaves of plants...		Summit crosses	Summit crosses by country	Summit crosses in France		The % symbolizes the fact that only a part of the objects is covered.
&aspect	Subcategories which include an additional aspect to the category scope		Mountains with snow	Mountains at sunrise by country	Water reflections of mountains in France		The & symbolizes the addition of a special aspect.
*special kind	Subcategories which limit the topic to a special kind of objects		Inselbergs	Inselbergs by country	Inselbergs in France		The * symbol is already widely used for such cases.
+location	Subcategories which limit the topic to a specific geographical area, if not collected in their own “by location” metacategory	Geography of Switzerland	Mountains of Austria	Mountains of Europe by country	Mountains of Bretagne	Mont Blanc in France	Think of the + as the cross to mark a location on a map.
>relation	Subcategories which are tightly related but nevertheless lead away from the actual topic, like views from a mountain, products of a company...		Views from mountains	Views from mountains by country	Things named after mountains in France	Views from Mont Blanc	Since it leads the user away from the actual topic, it's good that it's after most other special sortkeys. Also the > symbolizes the arrow pointing away from the topic.
?	Subcategories for items where the correct assignment is unclear, like "Unidentified XYZ"		Unidentified mountains	Unidentified mountains by country	Unidentified mountains of France		The ? is the logical key for unidentified items and already used widely.
@number	Subcategories naturally dividing the topic into subtopics, but with a non-alphabetic sort order, for example by season, by month...		Mountains in summer	Mountains in summer by country	Mountains of France in October	Mont Blanc in April	The @ gets sorted directly before A-Z, so it's ordered exactly where alphabetically sorted entries would be located.
A-Z	Subcategories naturally dividing the topic into subtopics, with an alphabetic sort order	Geographical modeling	Mont Blanc	Mountains of Italy	Mont Blanc	Geology of Mont Blanc	The natural sorting of subcategories.
~	Subcategories outside the topical category tree, linking to technical features of Commons like templates, gallery pages, meta categories	Geography templates	Categories by mountain		Gallery pages of mountains of France	Gallery pages of Mont Blanc	Doesn't actually contain media but other stuff, so mostly uninteresting for the average user.

Note the examples are only there to help understanding. Some categories are in fact not direct subcategories, but some levels lower, and some categories don't even exist.