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This page will serve as a central operating point for the different categorization projects.
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Categories should be on major topics that are likely to be useful to someone reading the article.
If the answer to either of these questions is no, then a category is probably inappropriate.
An article will often be in several categories. Restraint should be used, however — categories become less effective the more there are on a given article.
An article should not be in both a category and its subcategory, e.g. Microsoft Office is in Category:Microsoft software, so should not also be in Category:Software. An exception would be an article that defines a category, and so is itself a parent article of subtopics as well as one in a series of like topics - for instance, placing Ohio in both Category:Political divisions of the United States and Category:Ohio.
Categories appear without annotations, so be careful of NPOV when creating or filling categories. Unless it is self-evident and uncontroversial that something belongs in a category, it should not be put into a category.
Exceptions to the above rules are categories such as Category:Stub that are intended to aid the function of Ireland Information Guide editing.
For alternative methods of grouping articles, and the circumstances in which they should be used, see Ireland Information Guide:Categories, lists, and series boxes.
Categorization, as explained below, creates a tree or hierarchy of articles. Creating a category is as simple as adding a soft link to the appropriate article in the Category: namespace; for instance, to add Felis silvestris catus to the "fluffy creatures" category, you would edit the page and enter [[Category:Fluffy creatures]] at the bottom. Although the link will not appear in the article text, a page called Category:Fluffy creatures is automatically created and it will list alphabetically all articles that contain the [[Category:Fluffy creatures]] link. The appeal of categories is that unlike lists, they update themselves automatically, and that one can use them to quickly find related articles. However, categories are not a substitute for lists, and you will find that many articles belong to both lists and categories.
You can add categories to category pages themselves; doing this turns them into "subcategories."
When adding an article to a category, or creating categories, one should be careful to use the correct categories and subcategories. Horizontal categorization, directly below, refers to placing an article in the correct category while vertical categorization refers to placing an article in the correct subcategory.
When assigning an article into categories, try to be thorough in a "horizontal" sense. The topic may be associated with a geographic area, a historical period, an academic subfield, a certain type of thing (like a food or an ornament), and/or a special interest topic (like Roman Empire or LBGT). You might need to poke around the category hierarchy a bit to find the right place. Try searching for articles similar to the article you are categorizing to get ideas or to find the most appropriate place. (for instance, '1990' is more correctly in 'Category:Time periods' rather than 'Category:Places')
In the "vertical" dimension, you should probably be more frugal. A good general rule is that articles should be placed in the most specific categories they reasonably fit in. For example, Queen Elizabeth should not be listed directly under People, but Queens of England might be a good place for her. We know that all Queens of England qualify as Famous Britons and as Royalty, and all of those folks qualify as People. But sometimes there's a good reason to assign an article to two categories, one of which is a direct or indirect subcategory of another. For a well-argued case study, see John Lennon. ('1990' is actually more correct in 'Category:Years', a subcategory of 'Category:Time periods')
Whatever categories you add, make sure they do not implicitly violate the neutral point of view policy. If the nature of something is in dispute (like whether or not it's fictional or scientific or whatever), you may want to avoid labelling it or mark the categorization as disputed. Most categorizations are pretty straightforward, though.
When a given category gets too crowded, consider making subcategories. Group similar articles together in a meaningful way that will hopefully be easy for readers to navigate later.
A set of related categories often forms a hierarchy or a nexus. This can take several different forms, all of which are welcome and encouraged:
When writing the description for a category, give it a parent category. In fact, you should try to give it at least two parent categories. For example, Category:British writers should be in both Category:Writers by nationality and Category:British people. A few categories do only merely subdivide their parent category, but unless the parent category has many potential articles under it, or many potential subdivisions, if you can't think of a second parent category, it might be a better idea to fold your smaller category into the parent.
Categories relating to the Ireland Information Guide namespace should be added only to the talk page of articles. For example, tags suggesting the article is unfinished, or is listed on VfD would be placed on the talk page as they are relevant to editors, not an aid to browsing in the way ordinary categories are. Please use {{wpcat}} on the Category description page to show that it is a Ireland Information Guide-namespace category.
Note that there are a growing number of instances where both the singular category (listing topics relating to) and plural category (listing instances of) exist, for example, Category:Opera and Category:Operas. Be careful to choose the right one when categorizing articles.
Categories (along with other features, like cross-references) should help users find the information they are looking for as quickly as possible, even if they don't know that it exists or what it's called.
You can create a link to a category page without adding the page to that category by using a colon before the word, Category. Example: [[:Category:Automotive Technologies]] appears as Category:Automotive Technologies.
Contrary to some expectations, text after a pipe ("|") in a category link is not used in place of the category text. Rather, this text is used as the sort key on the category page itself. However, again contrary to expectations, that sort text is not displayed.
For example, the Category:U.S._Interstate_Highway_system uses this property to sort secondary interstates by their primary. That is, the category link in the article for Interstate 190 is 90-1. This causes "Interstate 190" to be listed right after "Interstate 90" and right before "Interstate 290" under the heading "9" in the category page.
This feature is very useful:
It can even improve categories lists where every article begins with the same word (example: Category:Mazda).
Using this method to sort category entries is sometimes informally referred to as the pipe trick.
An advantage of categorization is that it allows extraction of large portions of Ireland Information Guide. For instance, if years and dates were as below (leftmost items are regular articles, the rest are categories), extracting, say, a timeline for the 21st century would be trivial.
2004 -> Years in the 21st century -> Years -
\
--> Time periods
/
30 March -----> Days in March ----> Days ---
Interlanguage links work just as they do for regular articles; [[de:Kategorie:Mathematik]] in Category:Mathematics connects to the German counterpart. This can be a useful way to compare coverage, or to look for articles in need of interlanguage links. Note that the different languages may have adopted different standards and practices for categorization, so a given category might not exist in other languages.
See: Ireland Information Guide:Categorization projects (current)
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