Commons talk:Categories

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One-image categories?[edit]

I find nothing on whether or not we should create a category for only one single image. Has it been discussed and is there policy on that? --SergeWoodzing (talk) 09:18, 19 March 2016 (UTC)

I'd say it depends on the nature of the category.
Categories for notable people often make sense even for a single file. One reason for this is to allow categorisation under Category:People by name, which is only supposed contain other categories. Another is to allow separation between categories related to the person (e.g. year of birth, nationality, profession) from what's seen in a particular image (e.g. women with glasses, men with beards). If you apply those directly to a file instead of creating a category for the person, someone creating the category later on has to (1) have the initiative to search for other files to put in the newly created category (2) actually find the file (3) separate the categories pertaining to the person from the categories pertaining to the file itself (4) remove the former from the file (5) add them to the person category and (6) place the file in the category.
In some cases, even categories with zero files make sense. When I cleaned up Category:Districts of Stockholm, I created categories for all the districts, even if there were no files to place in them at the time. The category tree would not have been complete without them, and it was obvious that it was only a matter of time before they would be populated. Category:Lunda, which was empty for some time, now has a couple of files and even a subcategory. Category:Hansta is still waiting for its first file. Once someone uploads a relevant file, that greatly increases the odds that it will be correctly categorised.
Categories exist to help find existing files and to categorise new files. Overly specific categories that are unlikely to ever have more than one file are probably not useful for those purposes. LX (talk, contribs) 10:58, 19 March 2016 (UTC)
I agree with User:LX. Also keep in mind that categories on Commons are not comparable with categories on the Wikipedias. Most categories of current subjects will fill up with time when more photos are taken, since the number of possible photos of a subject is basically unlimited. At the Wikipedias, on the other hand, a certain subject only has a limited amount of possible encyclopedic relevant sub-topics. --Sebari (talk) 13:56, 19 March 2016 (UTC)
Thank you both! --SergeWoodzing (talk) 08:34, 20 March 2016 (UTC)

Spinning off new categories[edit]

At what stage should a new category be spun off? Consider the following example. Suppose that I find the category "Public libraries in the United States" has become too large. That category could then be broken down into 51 sub-categories – one for each state (counting Washington DC as a state). Since the United States and Luxembourg are both sovereign independent states, should I also break the category "Public libraries in Luxembourg" down into a number of sub-categories – one for each administrative sub-division of Luxembourg. I think that the answer is "No", but why not? The real answer, I believe, lies in the size of the resultant categories.

May I suggest that a as a guideline well-defined category that contains fewer than 10 images should not be broken up, one that contain 100 images should be broken up while discretion should be used for a category with between 10 and 100 images. Martinvl (talk) 07:14, 31 March 2016 (UTC)

The concept is reasonable, but putting hard numbers to it is a mistake as that may be interpreted as "must do" not "consider doing". It depends on the situation - sometimes a large number in a single category is OK, but sometimes a much lower number is not tolerable.
Also bear in mind these concepts are not always straightforward subdivisions of one large concept. For instance if there are just 5 images in "Libraries in Luxembourg" there still might be a real need for "Libraries in Luxembourg City", because "Buildings in Luxembourg City" has hundreds of files.--Nilfanion (talk) 10:06, 31 March 2016 (UTC)
There is no hard and fast guidelines of when to break down categories. Sometimes it is useful to create a category with only one file in it. Also, just because you subdivide the libraries in the US does not mean you have to do the same in other countries. Also remember that most categories will get more photos with time, so they will need to be split up eventually anyways. --Sebari (talk) 22:35, 31 March 2016 (UTC)