Category talk:Aircraft by registration

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Naming of subcategories[edit]

See CfD discussion (Sept 2009)


  • creation of category: 02 July 2009
  • 1990 subcategories - 02:25, 11 September 2009 (UTC)
  • 2390 subcategories - 18:26, 27 September 2009 (UTC)
  • 2600 subcategories - 2009 October 10 (rename of subcategories)
  • 2829 subcategories - 02:03, 13 October 2009 (UTC)
  • 4608 subcategories - 12:41, 14 November 2009 (UTC)
  • 5939 subcategories - 16:32, 28 March 2010 (UTC)
  • 6460 subcategories - 19:26, 18 July 2010 (UTC)
  • 7620 subcategories - 18:44, 4 September 2010 (UTC)
  • 8318 subcategories - 12:18, 4 January 2011 (UTC)
  • 8541 subcategories - 05:37, 10 March 2011 (UTC)
  • 9746 subcategories - 18:22, 22 September 2011 (UTC)
  • 38242 subcategories - 19 April 2014
  • 45218 subcategories - 15 August 2014
  • 50407 subcategories - 12 November 2014
  • 67791 subcategories - 22 October 2016

Category description[edit]

At Category:Aircraft by registration, I added a short summary about how the subcategories seem to work. This is probably not of much interest for the regular contributors, but can help newer ones like me. Please review it, edit it or suggest improvements here. -- User:Docu at 02:03, 13 October 2009 (UTC)

Military aircraft[edit]

I see subcategories for non-civil aircraft “registrations” are being created; I agree it is a good idea, however, I think the naming poses a small problem. The current naming, e.g. Category:10+21 (aircraft) might work for German aircraft, because of the strange pattern, but it can hardly work for other states. For instance, I guess there might be more airplanes with the “6052” registration number. So, how should its category be named? I was thinking about something like “CZ 6052 (aircraft)”, or something more verbose names like “6052 (Czech aircraft)”, “6052 (Czech military aircraft)”, etc. Comments, ideas? --Mormegil (talk) 16:33, 21 March 2010 (UTC)

So far I wasn't aware of the problem. There are a number of other countries with different patterns for military aircrafts, such as Category:Y1-111 (aircraft),Category:XH135 (aircraft), Category:T-336 (aircraft).But increasing the numer of categories for military aircrafts is raising the problem you described. I personally have no better idea as you propose as “6052 (Czech military aircraft)”, but I am not really happy with it. Has anyone further ideas? Gomera-b (talk) 16:55, 28 March 2010 (UTC)
I would suggest a new subcategory, like "Military aircraft by registration", since civilian aircraft generally have a predefined registry format that sorts well with one another, whereas military aircraft can be pretty much anything (iirc). Better to separate the two than mix together and muddy the proverbial waters. Huntster (t @ c) 20:12, 28 March 2010 (UTC)
Categorising military aircraft by serial number adds no value to commons. 99.9% of users will be looking for a German Air Force A310 not by serial, which in the example above is actually 1021 the cross is not part of the serial. MilborneOne (talk) 16:09, 6 June 2010 (UTC)

confusing category system[edit]

I re-added some of the aircraft type categories which were replaced with the registrations but have removed them from the A-BCDE registration categories. Having all the aircraft types in registration categories is very confusing and is making life very difficult for users trying to find images. I dont have a problem with registration categories but they should not replace the original type cats. It also removed another point of confusion in that the aircraft cats are not unique a registration can be used by many types which could cause for example a Boeing 707 to appear in the Boeing 767 category. By moving the type categories back to the image this is not a problem. Thanks. MilborneOne (talk) 16:09, 6 June 2010 (UTC)

I concur with User:MilborneOne, when looking for images to illustrate aircraft type articles on Wikipedia there is no way to find an image of the aircraft type unless it is categorized by aircraft type. Categories by aircraft registration may help the "plane spotters" but it greatly hinders writing an encyclopedia. - Ahunt (talk) 16:33, 6 June 2010 (UTC)
I agree that the aircraft type categories should not be removed from the image file pages, and should be restored where they have been removed. I have no problem keeping the reg cats if that is desired, though I don't know what the benefits of having categories for the registrations are. However, I can see where having actual pages for each registration number would be beneficial. This would allow photos to be added under headings for airports, incidents, and even separate aircraft types. - BilCat (talk) 17:06, 6 June 2010 (UTC)
So moving forward, perhaps the instructions on the main page should state that registration categories "must only be used alongside type categories, not in place of them." AKA, change the instructions so it no longer instructs users to place registration categories inside the type and airline parent categories? Huntster (t @ c) 18:11, 6 June 2010 (UTC)
Thanks Hunster I think that is all we are asking for in that the images appear directly in the type and airline categories. It would remove the problem of having to go through the reg cats to find images but these would still be available to find images by registration. MilborneOne (talk) 18:19, 7 June 2010 (UTC)
It would be awesome if a note about this (do not remove other plane description categories when registration-categorizing) can be put somewhere for new users like myself. Before I read this, was doing this a lot, removing type categories from images when adding registration categories. I might not be adding those categories to images I upload, but should not remove them from other photographs. Hhm8 (talk) 04:01, 4 September 2014 (UTC)
Symbol keep vote.svg  Agree I agree with you. Most of the images has only the "registration code" witch means very little to most of the people. I think it would be nice to keep at least the aircraft type (ex: Boeing 737) to avoid to go down one more sub-category to know it. The airline name is easy to see, because it is almost always painted in the aircraft. I know that this could be seen as over categorization, but I still propose this "policy". The categorization "by registration code" is good in terms of organization, but it is useless to anyone who just wants to browse the images to find a good one (note that it has now about 46 000 members and it is growing). NOTE: The CatScan is no more working --JotaCartas (talk) 05:03, 4 September 2014 (UTC)

If the registration is not unique, it should be put into Category:Re-used aircraft registrations. In these cases, either a sub-category for each aircraft should be made or the aircraft type and aircraft operator categories left with the images.

To view all images in a subcategory for an aircraft type, CatScan displays a complete gallery. -- User:Docu at 10:23, 8 June 2010 (UTC)

I think the aircraft type category should go only in the registration category, and not the image, to avoid overcategorisation. It's straightforward to add a link to CatScan to the top of each aircraft type and airline category, the {{Catscan gallery}} template does this. Benchill (talk) 09:35, 3 August 2010 (UTC)

categorize by registration[edit]

i think, this categorization is a product of brainless unwordly bureaucrats and complete unsuitable for commons or wikipedia (nobody, all over the world, search or respectively found - in commons or wikipedia - an image with such a category - its a nonsense and total unnecessary!). dontworry (talk) 07:44, 4 January 2011 (UTC)

Well, tell us how you really feel. :/ If you don't like it, then don't use it. Obviously there are others who do find it useful. It's whole point is to collect pictures of the same aircraft into a single category. Huntster (t @ c) 07:57, 4 January 2011 (UTC)
i'll give you some example of search, resp. found problems with that categories, if i wish to know, what type of airplane it is or in which article i can found (more) information about the airplane: [1], [2], [3], [4], etc., etc. in all that cases, i'll get only bull-shit and nothing information! dontworry (talk) 09:00, 4 January 2011 (UTC)
If you feel that the images are not being properly categorised, then that's one thing, and you can suggest ways to improve the system. It'll never be perfect, but like any wiki project, we're constantly improving. These aircraft registration categories are for one specific thing: to collect images of the same individual aircraft. They should be independent of all other "flexible" descriptive categories (such as colour, type of view, etc.), and should only be subcategories of elements that never change (typically just model). Of course, that doesn't always happen, and some folks have a bad habit of stripping all descriptors from the images and using just the registration number as the sole category, but that isn't the norm. I'm sorry that you've had a bad experience with this, but don't condemn it just because you don't like it. Huntster (t @ c) 10:18, 4 January 2011 (UTC)
it could't be work, otherwise you doesn't categorize any person with its National identification number or blood type, fingerprints etc. that also doesn't work (for searching in commons or wikipedia)! that's maybe useful for flight-engineers and other professionel stuff around airplanes, but not here. dontworry (talk) 11:08, 4 January 2011 (UTC)
I'm afraid I don't really understand your statement; we organise people by their names, and for aircraft and vessels, their registration numbers are their "official" names. Like I said before, these categories are strictly used for grouping images of the same aircraft. Huntster (t @ c) 12:03, 4 January 2011 (UTC)
Personally, I don't think navigation say from File:C-17_conducting_maneuver_Wings_Over_Wine_Country_2007.JPG to Category:C-17 Globemaster III (United States Air Force) through Category:5N-MJO_(aircraft) is really easy. Template:Infobox aircraft image (sample) somehow makes it easier, but requires significant edits to the file description. --  Docu  at 12:18, 4 January 2011 (UTC)
I can see that, and personally speaking, I would prefer if these categories had *no* parent categories other than this one. I think they should be standalone holders, strictly for sorting by individual aircraft, but that's not how it's evolved. I'd certainly support any proposals that were to bring current usage into line with that ideal, though. Huntster (t @ c) 12:33, 4 January 2011 (UTC)
I understand the reasoning (and I agree somewhat), but… what is the difference between an aircraft registration category and any other category on Commons? As a completely random example… “if i wish to know, what stadium it is or in which article i can found (more) information about the place”, what should I do with File:Rsca4.JPG? We know the categorization system on Commons is far from perfect. If you want to make a complete revolution in the system, go ahead, try to invent something better. But I don’t think doing one tiny part of the category tree differently from the rest is the best idea. --Mormegil (talk) 18:13, 4 January 2011 (UTC)

Nothing against a Cat Airplanes by Registration, but it is totally senceless to create so much one-file cats. So find an alternative way in the next 4 weeks, otherwise this one file cats will be deleted. Everyone can search by Airline more comfortable.Sandmann4u (talk) 18:36, 1 April 2011 (UTC)

You can not search by airline if the aircraft is not owned by an airline – which is the case for most single-engine aircraft, since they are usually privately owned … --El Grafo (talk) 08:51, 2 April 2011 (UTC)
But wouldnt it be better to change the meta-cat to ordinary cat? so the problem wo too much one-file cats is solved and your reason is still included.Sandmann4u (talk) 09:09, 4 April 2011 (UTC)
I'm not sure if I understand you correctly, so let's set an example:
I don't see any problem with one-file cats, as long as they are only a subcat of the "by registration" tree. But when you are looking for a good picture of an aircraft type or an airline and the whole type-/airline-cat does only consist of one-file registration-subcats, it's kind of annoying (see Category:Cessna 172)). So, what about some kind of guideline that says "only use registration-cats in type-/airline-cats if it contains at least n files"? (As a value for n I would propose 5). Because in my opinion it does make sense to use Category:D-AQUI (aircraft) as a subcat of Category:Junkers Ju 52.
Another thing we could try is to create a new subcat like Cessna 172 by registration for every type/airline, but I'm not really sure if I would like that → could create even more trouble --El Grafo (talk) 10:06, 4 April 2011 (UTC)
Until we have a "images of category depth = n" switch on category displays, Catscan might help. --Foroa (talk) 10:21, 4 April 2011 (UTC)
The rule of the type "if it contains at least n files" could work if we decided to stop accepting new files, but if we try to establish a basic system that can grow further, it's not that easy. Personally, I think it's a pleasant surprise if I notice that we got further images of the same aircraft by a different uploader.
Following Foroa's suggestion, we could add {{catscan gallery}} to Category:G 103 Twin Astir. This should solve the issue. --  Docu  at 10:45, 4 April 2011 (UTC)
OK, good point. Within smaller type-cats it shouldn't be a problem to wait until there are at least n pics of plane XY and then switch over to using the registration-cat as a subcat, but I admit that you might easily loose overview in the bigger type-cats. Regarding {{catscan gallery}} please see my comment below. --El Grafo (talk) 12:28, 4 April 2011 (UTC)

Gern auch auf Deutsch... My opinion is to take this pictures of this one-file cats directly into cat aircraft by registration. If there are more pics of an airplane. nothing against subcats.Sandmann4u (talk) 10:55, 4 April 2011 (UTC)

No, this parent category should never have individual images in it. It's a meta category. Rather than limiting inclusion in subcats to n files, as I've said above, I would like to see these subcats not included in any other category than this one (and similar categories like Category:Gliders by registration), so that the issue of Category:Cessna 172 doesn't occur. Huntster (t @ c) 11:04, 4 April 2011 (UTC)
As stated above, I think there are some cases where registration-cats as a subcats of type-cats do make sense (eg. Category:D-AQUI (aircraft)). Nevertheless, I could live with the decision not to use registration-cats in type-/airline-cats or Foroa's suggestion to use {{catscan gallery}} – but I think we should a) decide for one of these alternatives, b) promote that at Category:Aircraft by registration and c) stick to it. --El Grafo (talk) 12:28, 4 April 2011 (UTC)

categorize by registration: Type → Type by registration → A-BCDE (aircraft)[edit]

Another idea (let's take the Cessna 172 as an Example):

Symbol support vote.svg 

you don't have to browse the registration-cats when you are looking for a pic of the type
Symbol support vote.svg the type-cats won't become crowded/confusing because of the many registration-cats
Symbol support vote.svg you still can get from the registration to the type easily
Symbol oppose vote.svg this would mean we'd have some kind of "double-categorization"
Symbol oppose vote.svg awful lot of work to restructure existing cats

Comments? --El Grafo (talk) 12:04, 17 August 2011 (UTC)

Definitely support, as it would clean up these parent categories that are, in some cases, wildly overcrowded with registrations. I wouldn't worry about the semi-double-categorisation, as this provides a net benefit. Huntster (t @ c) 11:18, 18 August 2011 (UTC)
Well, if you imagine some other possible "by-"categories like those we already have in Category:Aircraft (such as type by color or type by operator), that double-categorisation becomes even less daunting to me. But let's hear some other opinions first … --El Grafo (talk) 08:53, 19 August 2011 (UTC)
I would support the change, as you can see from previous comments it is difficult at the moment to find images of a particular aircraft without browsing the reg cats which is a bit of a drudge. Also the registration cats would still be a sub cat of aircraft registered in foo cats if you really want to go down the cat tree by registration. MilborneOne (talk) 10:36, 21 August 2011 (UTC)

What I hadn't thought of when proposing this: The amount of work/time needed to restructure/recategorize the existing cats will be HUGE. Just have a look at Category:Airbus A320: There would be >500 R-EGIS (aircraft)-cats to be moved to Category:Airbus A320 by registration. And each of them would have to checked for images that are not yet directly in Category:Airbus A320. Maybe this could be partly done by a bot, but I have no experience concerning bots. Any ideas? --El Grafo (talk) 12:01, 21 August 2011 (UTC)

Yes, this should easily be done with a bot. When/if the proposal is accepted, you could seek out one of the main members of the bot group for advise, laying out exactly what needs to be accomplished. For that matter, you might invite them here while the discussion is on-going to state what is possible and what isn't. Huntster (t @ c) 05:25, 22 August 2011 (UTC)
Everything is better then the current system. Sandmann4u (talk) 13:07, 19 September 2011 (UTC)
Symbol support vote.svg  YES : there have been many occasions when I was loking for certain type of airbraft from a certain airline in order zo illustrate an article. The current system makes it very difficult (or you have to use CatScan) to find the required pic. -- Wo st 01 (talk / cont) 14:27, 19 September 2011 (UTC)
Personally I don't mind if they are listed both in Category:Cessna 172 and the more technical registration-cats (e.g. Category:C-FCWD (aircraft)), but I'd avoid creating an intermediary step "Category:Cessna 172 by registration". --  Docu  at 18:21, 22 September 2011 (UTC)
Pictogram voting comment.svg  Comment I am aware of the problems of the current system but there are also some problems with the proposed system:
  • It is against the general practice to avoid placing images both in a parent and a child category. Of course, these policies are not carved in stone, and we could make a well-founded exception in this policy. This could, however, lead to unnecessary edits when users unaware of that exception would remove files from parent categories, and the others reverting their edits.
  • It can lead to over-population of aircraft type or airline categories. (There would probably be hundreds or even thousands of files in a category of some common aircraft type.) Maybe this could be avoided with "aircraft type by airline" categories (e.g. Category:Boeing 737-800 (Air Berlin)).
Galleries could be one way to make it easier to find files even in the present categorizing system. E.g. we could pick the best images of each aircraft type and each airline to aircraft type (e.g. Airbus A320) and airline galleries (e.g. Finnair). ––Apalsola tc 19:24, 23 September 2011 (UTC)
Galleries could certainly be made better to find images but it would be better to try and sort the categorisation. Another annoying factor is when you have a Category:A-BCDE (aircraft) it is placed both in an airline and type parent category, this gets confusing because more than one airline may have used the aircraft and aircraft registrations are not unique and can be used on a number of different aircraft. The original scheme before the reg cats were added was to have a cat on each image for the type and operator, this was far better so as a default perhaps we should just go back to the original system. MilborneOne (talk) 20:38, 24 September 2011 (UTC)

Hello - anybody care that the system doesnt work? MilborneOne (talk) 17:36, 14 October 2011 (UTC)

I notice that because it is hard to find any aircraft with the registration system users are now creating for example Air France Airbus A380, Airbus A380 by location as well as Airbus A380 by registration. In the old simple days an image was categorised by type/user/location, simple. The new system will create thousands of categories like Category:Foo aircraft at Foo Airport operated by Foo airlines and at a simple guess of 10,000 aircraft types multiplied by tens of thousand of users and then possibly every landing field, airport, airbase in the world is a big mess. But as nobody appears to care about the confusion caused perhaps it is time to give up and move aircraft images to the country wikis. MilborneOne (talk) 17:44, 14 October 2011 (UTC)
Still no suggestions to sort out this mess? MilborneOne (talk) 20:33, 30 November 2011 (UTC)
Sorry, at the moment my time for wikipedia/commons is nearly down to zero due to "real life" work → no suggestions from me atm :-( --El Grafo (talk) 21:18, 1 December 2011 (UTC)
FYI: I left a note at the recently created WikiProject Aviation – maybe this brings us some new ideas. --El Grafo (talk) 12:47, 9 December 2011 (UTC)
In the section "confusing category system" above, four editors argued for placing aircraft type/model cats against each image file, and one editor argued against. Some editors are currently deliberately removing type/model cats from image files (eg here) - surely admins should be chasing those down, until we get some better resolution here. PeterWD (talk) 14:26, 17 December 2011 (UTC)

Category:C5-FBS (aircraft)[edit]

is the Category:C5-FBS (aircraft) correct? But the aircraft has change the registration in the past. --Atamari (talk) 12:18, 6 June 2012 (UTC)

and Category:HR-AMW (aircraft)? --Atamari (talk) 12:23, 6 June 2012 (UTC)

Categorizing aircraft which are no longer registered the same as when image was taken[edit]

There is the category "Re-used aircraft registrations". This is used when there are multiple aircraft which had a registration. However, this gives no information as to which aircraft, if any, do not have this registration anymore. It would be nice to have a way to find out this information. A category to put the photos of aircraft which no longer have that registration in would be neat. For now, I will be use Category:Unregistered aircraft, (which hopefully does imply that the aircraft which had that registration was subsequently reregistered or deregistered); a better name would be welcome, and if one is decided upon then Unregistered aircraft can be redirected, and all its subitems moved, to that newly-named category. Hhm8 (talk) 05:16, 4 September 2014 (UTC)

  1. In an aircraft context, the term "unregistered" means an aircraft that is simply not registered, so applying it to an image of an aircraft with a valid or visible registration is illogical and misleading.
  2. The Federal Aviation Administration uses the term "deregistered" in the way that this "Unregistered aircraft" category is defined, but that is very country specific.
  3. In descriptions and categories at Wikimedia Commons, there should be no sense of 'now', 'currently', 'today', or 'this year'. Images from photography represent instant (or near) snapshots in time, so descriptions and categories should not need to be updated to reflect later events. We have already had POV partisans and nationalists attempting to rewrite history here, by deleting or modifying stuff relating to countries that no longer exist as such (eg Yugoslavia).
  4. The primary purpose of categorising here is to facilitate the finding of files via a hierarchical schema - see COM:CAT and COM:SCOPE. I can't see how current categories "Unregistered aircraft" or "Re-used aircraft registrations" serve that purpose. Surely the latter category should be wholly redundant, if all such registration categories have sub-cats for different aircraft (some do, some don't), in the strict application of the hierarchy schema used here - see also COM:OVERCAT.
  5. If we rigorously apply such a concept as deregistered aircraft, then every single registration category (currently over 50,000) would need to be constantly monitored against all international aircraft registers, and all of them would need to be amended eventually, after today's aircraft end their active lives. Personally, I regularly analyse the FAA current and deregistered files for changes for one specific aircraft type, via database software and programming techniques. I doubt that many other people have similar means or the initiative/dedication, but volunteers, step forward in your thousands.PeterWD (talk) 13:26, 14 November 2014 (UTC)
Thanks for the reply. Don't have time now for a detailed reply, but in short: (1) i agree with some of what you said, (2) wikidata combined with categories may be the best way of keeping this information --Hhm8 (talk) 12:04, 9 December 2014 (UTC)

Categorisation by manufacturer serial number[edit]

I'd like to categorise aircraft by the manufacturer's serial number. I was looking at a photo from the @commonsaviation account, of an RAF TriStar tanker, and had to take some time to find out who it was delivered to and what its registration was (ZD-951, formerly G-BFCD for those interested). Its serial number was 1165, and it would be nice to have a category like Category:Lockheed TriStar MSN 1165 or similar, under which Category:G-BFCD (aircraft) and Category:ZD951 (aircraft) would appear, providing a clear, coherent method with which to follow an aircraft throughout its life.

TLDR - can we use manufacturer's serial numbers for planes in the same way we use the IMO number for ships. Thanks. Nick (talk) 00:08, 16 November 2014 (UTC)

In a way your proposal sounds interesting. But of course MSN is not comparable to IMO. IMO is unique and MSM is not. MSN is more compareable to yard-# with ships.
Using MSN needs to know manufacturer and aircraft type in addition (as you showed here:Category:Lockheed TriStar MSN 1165. I face some problems doing like this. I.e. manufacturers name has changed over the production period. How will we handle this. Or mixing up types (which will happen) will create totally wrong Caregories.
What about just usung a new Category:MSN 1165? In case this is assigned to more than one aircrafts, it is rather easy to find what you want.
So my proposal, in case MSN is meant to be a usefull data in Cat-System, let us start simple with just MSN as additional Cat. (see above). --Gomera-b (talk) 12:29, 16 November 2014 (UTC)
FWIW, there is already Category:Aircraft by serial number that appears to serve the 'wish'. However, it has not seen any use since soon after its creation, and personally I have expressed my doubts about its usefulness. For example, surely the MSN (or c/n or cn) cannot be directly related to an image, but only via a registration (or military serial) category, otherwise how can we know that they are related. In the example case of the Tristar, my practice would be to put the military serial cat under the civil registration cat, or vice versa.PeterWD (talk) 16:23, 16 November 2014 (UTC)


Category:Aircraft by registration[edit]

This meta category has amassed 77,326 subcategories and needs diffusion. Part of the problem is that for quite some time there have been several subcategories in Category:Aircraft by registration by type following the scheme of "Boeing 747 by registration" and the like, but people still keep adding both Category:Aircraft by registration and "Category:<Aircraft type> by registration" to the main categories where individual aircraft by registration are gathered. E.g. Category:EC-MLD (aircraft) is categorised both in "Category:Aircraft by registration" and "Category:Airbus A321 by registration". Contrary to COM:OVERCAT this seems to be the rule at aircraft categories rather than the exception. I am presenting this issue here because Ardfern suggested that it be discussed with Commons:WikiProject Aviation only. However, I don't think that local consensus can trump a Commons-wide policy, so exceptions need to be approved here. De728631 (talk) 16:45, 2 April 2018 (UTC)

Why does a function (set) with 2 parameters - "Aircraft (by registration, by type)" have a superfunction (superset) with 1 parameter - "Aircraft (by registration)"?
To display all parents click on the "▶":

--Fractaler (talk) 09:35, 3 April 2018 (UTC)

That is how Wikimedia categories work. We define more specific categories the further we go down the category tree, and that means that more parameters come into play while the definition set out in a simple top category still remains valid for all elements further down the hierarchy. "Aircraft by registration" is for images where just the registration number is known. "Aircraft by registration by type" is a container for aircraft categories where the registration and the type is known, and "Category:Kawasaki C-1 by registration‎" and the like would be the next level. The problem, however, is that subcategories should only be part of one category level further up the direct line, and not be sorted into two related parent categories. De728631 (talk) 21:07, 3 April 2018 (UTC)
Having so many entries isn't always a reason to diffuse a category. This isn't a standard-type category. Another example of this type of category is Category:People by name, which has even more entries: 366,781 when I checked just now. There are categories that are subsets of that one, such as Category:Men by name and Category:Women by name (see Category:People categories by name for others), but the contents of those categories are also in Category:People by name. We should handle similar categories such as this one the same way. --Auntof6 (talk) 04:36, 4 April 2018 (UTC)
First, what is a "category tree"? If it is a taxonomy , then we have: ROOT <- 1) SUBROOT1 (by A); 2) SUBROOT2 (by B); 3) SUBROOT3 (by A, by B). Examples: "Aircraft by parameters" <- 1) "Aircraft by registration"; 2) "Aircraft by type"; 3) "Aircraft by registration by type" --Fractaler (talk) 08:28, 4 April 2018 (UTC)
Don't place an item into a category and its parent. For example, a black and white photo of the Eiffel Tower should be placed in Black and white photographs of the Eiffel Tower. It should not be placed in both that category and the Paris category at the same time.
Maybe I didn't make it clear enough when I started this discussion, but my main concern is not so much the way we may want to diffuse this category in the future but a massive case of overcategorisation right now. Contrary to the Commons policy on categories, there are probably hundreds of subcategories that are placed into a category and its parent. So my approach is to remove all those subcategories from Category:Aircraft by registration that have already been sorted into a category "by registration by type". This is the commonly accepted standard to solve the issue, but it has been challenged in this case and needs discussion. De728631 (talk) 09:50, 4 April 2018 (UTC)
We have now, for example, 3 sets: 1) Category:Aircraft by registration, 2) Category:Aircraft by type, 3) Category:Aircraft by registration by type (the same for Category:People by name, Category:People by gender, Category:People by name by gender, etc.)‎. So, category tree (by the commonly accepted standard) must be ...? --Fractaler (talk) 10:38, 4 April 2018 (UTC)

Isn't this obvious? The category tree should be:

De728631 (talk) 12:11, 4 April 2018 (UTC)
Category:Aircraft by registration, however, may very well contain registration categories like "Category:D-ECAB" if the aircraft type is unknown. Once the type becomes known, the registration category should be placed into "<Aircraft type> by registration" instead. De728631 (talk) 12:15, 4 April 2018 (UTC)
Level 4 - you are right, here COM:OVERCAT. But also I mean (level 2->level 1), why the set Category:Aircraft by registration by type must be a subset of the set Category:Aircraft by type (or Category:Aircraft by registration)
To display the taxonomy below click on the "▶":

?--Fractaler (talk) 13:58, 4 April 2018 (UTC)

For the record, we agree on COM:OVERCAT. As to your question: It is the logical taxonomy for breaking down Category:Aircraft by registration and Category:Aircraft by type. Category:Airbus A380 by registration, Category:Jetstream 31 by registration etc. need to have parent categories and it would be improper to put them directly into Category:Aircraft by registration and Category:Aircraft by type because there are dozens of these "by registration by type" categories. A meta category for hosting them is not only justified but needed to make things more accessible, so that is how the connection between Level 2 and Level 1 works. De728631 (talk) 15:09, 4 April 2018 (UTC)

I'm going to ignore the application of set theory above (IMO it isn't an appropriate model for Commons), as abstract theory is unlikely to be informative to a specific problem.

I will stick to practical concerns. Say I have a photo of the plane with registration G-BOAC. I don't have a clue what sort of plane that is, but if I create its category I can place it in Category:Aircraft by registration based on what I do know. Alternatively, imagine I am seeking images of G-BOAC. I know its registration, so its reasonable to use Category:Aircraft by registration to try to locate it. If its directly in that category, I can find it. If its buried in a "by type" subcategory I cannot find it, as I do not have that information. In both cases, having the individual plane's category in Category:Aircraft by registration is helpful. Removing it from that category is harmful.

To put this a different way, "I want a plane with registration G-BOAC" is not sensibly narrowed down by instead saying "I want a Concorde with registration G-BOAC". In contrast "I want a Concorde" is sensibly refined with "I want a Concorde with registration G-BOAC". That suggests Category:Aircraft by registration by type should be a subcat of "by type" but not "by registration".--Nilfanion (talk) 20:39, 4 April 2018 (UTC)

If you're looking for a specific category G-BOAC, your first start should be the search field anyway. It will guide you directly to the desired category without you having to browse the category tree. It is the fastest solution for "I want a plane with registration G-BOAC", so a direct entry in Category:Aircraft by registration is therefore not even necessary. Also, Category:Aircraft by registration by type includes the "registration" element, so the question would still arise why it is not linked back to Category:Aircraft by registration. Per our category policy, "each category should itself be in more general categories, forming a hierarchical structure." The hierarchical structure would be broken if Category:Aircraft by registration was not involved. Pinging @Joshbaumgartner: who created "by registration by type" as he might want to comment here too. De728631 (talk) 23:24, 4 April 2018 (UTC)
PS: What I'm trying to demonstrate is that navigation in the category realm works both ways, not just top-down. So if I want to browse back from G-BOAC via "Concorde by registration" and further up the tree, I should be able to arrive at "Aircraft by registration" as well. De728631 (talk) 23:31, 4 April 2018 (UTC)
With bottom-up navigation, you can get to Aircraft by registration by some obvious logical route, no matter how its categorised. That is not true for top-down navigation unless it is directly in by registration. Breaking registrations down by type is simply NOT helpful for navigation. Outright deletion of by registration by type is preferable to have it messing up the utility of the by regisration category.--Nilfanion (talk) 16:39, 5 April 2018 (UTC)
Now you are contradicting yourself. A few paragraphs further up, you suggested that "Category:Aircraft by registration by type should be a subcat of 'by type'" rather than by registration while you are now outright opposed to "Breaking registrations down by type"? De728631 (talk) 18:30, 5 April 2018 (UTC)
Uhh.. '"by registration by type" should be a subcat of "by type" rather than "by registration"' is consistent with 'don't break registrations down by type'? The latter statement is stronger, but doesn't contradict the former. If you already know the registration, adding in the type of aircraft doesn't narrow things down further, you already have a unique plane. (As an aside, to me "aircraft type" implies things like "helicopter" or "wide-body airliner" not "Boeing 777"). What benefit is there to any user in removing categories like Category:G-BOAC (aircraft) from Category:Aircraft by registration? IMO the only logical subcats for aircraft by registration are for the countries of registration. That would link all G registered planes together, and would allow G-BOAC to have a sortkey starting with B instead of G - making it slightly easier to find in the still huge list.--Nilfanion (talk) 19:16, 5 April 2018 (UTC)
We do have country-specific categories. Category:Aircraft registered in the United Kingdom is a parent for all G- registration categories, and there are lots of other such categories for more or less any registration prefix. And "type" is the official ICAO designation for what may otherwise be called an aircraft model. Using "model" for general aircraft categories is problematic though, because it should only be used for categories of scale models. Hence the "by type" wording of the subcategories that was rightfully introduced by Uli Elch. De728631 (talk) 19:47, 5 April 2018 (UTC)
And those are the only ones that logically belong under by registration. As they are aspects of aircraft registration, not an otherwise unrelated aspect of aircraft.--Nilfanion (talk) 20:06, 5 April 2018 (UTC)
Are you sure?
Aircraft by registration
`-- Aircraft registered in the United Kingdom
`-- Aircraft registered in France
That way you would empty "Aircraft by registration" of all registration categories, because per COM:OVERCAT they would have to be sorted into the relevant country-specific subcategories, leaving you again with no direct search options. At the moment, "Aircraft by registration" and "Aircraft by registration country" are at the same level in Category:Aircraft registrations and that is a good structure. De728631 (talk) 20:37, 5 April 2018 (UTC)
And I agree with that structure. My point there is if we don't want to merge those two related concepts (the registration code and the registration country), why would we want to link two entirely unrelated categories?--Nilfanion (talk) 21:23, 5 April 2018 (UTC)
I do not understand what "specific problem"? Where can user place Category:G-BOAC (aircraft) based on what user do know or how can user find Category:G-BOAC (aircraft)? Who is the taxonomy for, who is the end user? What is the problem: creating a taxonomy or navigate (by navigator!) through it? Also, just for clarification: set theory is not a model. --Fractaler (talk) 08:42, 5 April 2018 (UTC)
Specific as in actually discussing the particular concern raised. Not discussing general points which could equally apply to any category. The application of set theory to Commons categories is the problematic case. Its based on the assumption that subategories must be subsets. That's clearly not true in many cases.--Nilfanion (talk) 19:16, 5 April 2018 (UTC)
Erm, if a subcategory is not a subset of its parent categories, where is the navigational benefit? Categories in a category tree shall "reflect a hierarchy of concepts, from the most generic one down to the very specific". De728631 (talk) 19:47, 5 April 2018 (UTC)
See this discussion. The navigational benefit is from linking two related concepts, but that relationship is not necessarily that between a set and its subset. The photos of a building in a city are a subset of the photos of the city. The photos of a building built by an architect are not a subset of the photos of the architect.--Nilfanion (talk) 20:06, 5 April 2018 (UTC)
"See this discussion." TLDR, and too much set theory. Still, there is a relationship between the architect and his buildings, so the photos of buildings are a subset of images related to the architect. De728631 (talk) 20:37, 5 April 2018 (UTC)
The short version is that the real issues start to appear at the 2nd order. The building could easily be a subcat of an entirely different city (the birthplace of the architect). That relationship is tenuous, but the two steps to get there are perfectly valid. Its conceivable that someone would place a photo of the building directly in the architect's category; its implausible that they would place it in their birthplace's category. That relationship is clearly not a strict subset-of-subset relationship, in contrast to building-city-country which would be.--Nilfanion (talk) 21:23, 5 April 2018 (UTC)
"Its based on the assumption that subategories must be subsets": first, its based on the assertion that must be a definition ("by list" or "by giving a property"). So, still no definition "by list" or "by giving a property". Also here, " The photos of a building in a city" (Category:Buildings by city? Category:Photos of buildings in a city?) - where can we read the definition of this term? When there are no definitions, then there are disputes. Do we need disputes? --Fractaler (talk) 08:13, 6 April 2018 (UTC)
Set theory is nice, but should not trump what works best for a real application on Commons. Josh (talk) 21:33, 8 April 2018 (UTC)
What does "works best for a real application on Commons" mean? As can be seen from the template with the taxonomy above, for example, in Category:B-6140 (aircraft) -> Category:Aircraft by registration -> Category:Aircraft registrations -> Category:Aviation data -> Category:Data, set theory is simply not used ("B-6140 (aircraft)" is not "Data"). --Fractaler (talk) 07:07, 9 April 2018 (UTC)
@Fractaler:: What is your proposal then? Which of the links you listed is invalid and should be broken? Josh (talk) 22:19, 9 April 2018 (UTC)

We should retain current use of Category:Aircraft by registration. It is an index of all aircraft registrations, regardless of further sub-categorization that can occur. Sub-categorization can be done by type, by country of registration, or by any number of other criteria. It is best if a registration is accurately categorized by all relevant methods, not just one. However, none of that changes the fact that it is both valuable and without harm to have an index that retains a link to all registrations. Since it does no harm and provides value, the current structure and method of using Category:Aircraft by registration should be retained. Josh (talk) 21:33, 8 April 2018 (UTC)

Category:Aircraft by type must be a subcategory of Category:Aircraft by registration? --Fractaler (talk) 07:07, 9 April 2018 (UTC)
Now that would be ridiculous. De728631 (talk) 12:21, 9 April 2018 (UTC)
@De728631:: It is ridiculous. Category:Aircraft by type is NOT a subcategory of Category:Aircraft by registration, nor should it become one, nor is anyone proposing that. As I stated above, we should retain current use of Category:Aircraft by registration. Josh (talk) 22:19, 9 April 2018 (UTC)

FYI, I have opened a CFD on this, so that people who follow category discussions will see it. --Auntof6 (talk) 16:00, 9 April 2018 (UTC)

Please see discussion at Commons talk:Categories#Diffusion of Category:Aircraft by registration. Auntof6 (talk) 15:51, 9 April 2018 (UTC)

Moved discussion text to this page so it will reflect in real time on both Commons talk:Categories and Commons:Categories for discussion. Josh (talk) 21:45, 9 April 2018 (UTC)
  • There is no problem with having all single-aircraft registration categories in the main "Aircraft by registration" acting as a super-category. This is not uncommon practice. A standardisation of the "by type" subcategories is always a good thing, of course. Huntster (t @ c) 19:25, 9 April 2018 (UTC)

There are some valid reasons to rethink exactly how Category:Aircraft registrations is structured. Never mind the hashing about whether or not a guideline is being obeyed or whether we are properly applying set theory, none of that is terribly valuable. The category does however beg some more clarity and streamlining. There are a couple issues which we can deal with in pieces, or as a whole. Josh (talk) 23:22, 9 April 2018 (UTC)

1 - xxxx (aircraft) categories are aircraft registrations, not aircraft. However, they are often treated as aircraft, especially since they say 'aircraft' parenthetically. This is not a problem for most common usage, but is exposed in corner cases and when analyzing the category structure. Keep in mind an aircraft may be assigned several registrations over its life, and some registrations may be assigned to different aircraft over time. Specific sub-categories of an aircraft registration category can be created to show its application to different aircraft (e.g. Category:N305FA (aircraft) into Category:N305FA (Boeing 737) and Category:N305FA (MD-83)). Proper names should be 'Aircraft registration N305FA' with sub-cats 'Aircraft registration N305FA assigned to Boeing 737 c/n 28662' and 'Aircraft registration N305FA assigned to MD-83 c/n 49398'. I am not proposing renaming these categories, unless someone is up for moving 75,000+ categories. The current abbreviated names are fine, but we should have a better description of what exactly those categories cover.
2 - Category:Aircraft by registration is named incorrectly. As noted above, the sub-cats are aircraft registrations, not aircraft, so the correct title should be Category:Aircraft registrations (flat list) or some other such appropriate title to indicate it is an index of all aircraft registrations ordered alpha-numerically. As it is, the current name adds to the confusion referred to in note 1 above. It may be appropriate to make this category a hidden cat while we are at it. Once this is done, sub and meta cats can be moved directly under Category:Aircraft registrations.
3 - Military identification numbers are not consistently treated. These are sometimes treated as aircraft registrations and other times as serial numbers or some other unrelated tree. Category:Aircraft registrations should cover all individual aircraft identifications assigned by authorities, military or civil. Sub-categorization can break down between assigning authorities for those that it is helpful for, but not all users will know what the issuing authority is for a particular identifier. No rename is needed, but a better description is required to make it clear what the category covers.
4 - Category:Aircraft by registration country is named incorrectly. As above, a more clear and concise name should be used, such as Category:Aircraft registrations by country of issue, to make it clear that the items within are aircraft registrations and that they are ordered by the country which issued the registration. It should be listed directly under Category:Aircraft registrations and not under Category:Aircraft by registration/Category:Aircraft registrations (flat list). Category:Aircraft by registration continent should get similar treatment, though 'continents' do not issue registrations, countries do.
5 - Category:Aircraft by registration by manufacturer and type are incorrect. They should be renamed Category:Aircraft registrations by aircraft assigned and sub-cats of that can parallel the categorization of Category:Aircraft to the level appropriate. Category:Aircraft registrations by aircraft assigned should be directly under Category:Aircraft registrations.

Some tweaks like these would allow the continued use of aircraft registration categories essentially as they have been used for the 75,000+ registrations in place, while at the same time adding clarity and cleaning up the structure of the category quite a bit. They will hopefully go some way to satisfying concerns over COM:OVERCAT and the set theory issues raised by De728631 (talk · contribs) and Fractaler (talk · contribs). Josh (talk) 23:22, 9 April 2018 (UTC)

"What is your proposal then?": set theory requires a definition, and therefore here, in the disputed case, it makes sense to give definitions to the term. What definition should the term "B-6140 (aircraft)" have for a more general term to be the term data"? The same for "aircraft by registration", "aircraft registrations", etc. --Fractaler (talk) 07:22, 10 April 2018 (UTC)
@Fractaler: As stated in the list above, definition of Category:B-6140 (aircraft) is an 'aircraft registration'. Not sure what definition you are looking for beyond that. Josh (talk) 16:46, 10 April 2018 (UTC)
I don't think we need to differentiate between xxxx (aircraft) and xxxx (aircraft registration) and all subsequent namings. Apart from Category:Temporary aircraft registrations that are used for test and transfer flights, registrations are seldom changed over the life of an aircraft frame and the registration is therefore often synonymous with the single airframe it got assigned to. We already have Category:Re-used aircraft registrations and its appropriate sub-categories as you showed above.
@De728631: You are incorrect that registrations are seldom changed; it is common practice to change a commercial aircraft registration several times during its life, especially when it changes ownership. I would not advise eliminating the existing sub-categorization of xxxx (aircraft) into xxxx (specific aircraft) categories. Assuming synonymy between an aircraft and its registration is a mistake. As stated, I am not proposing that these categories be renamed, but merely that we have better definition of them as being specifically related to that aircraft registration. Josh (talk) 16:46, 10 April 2018 (UTC)
Well, you wrote "Category:Aircraft by registration is named incorrectly. ... the correct title should be Category:Aircraft registrations (flat list) or some other such appropriate title", or "Category:Aircraft by registration by manufacturer and type are incorrect. They should be renamed Category:Aircraft registrations by aircraft assigned". Isn't that renaming? Apart from Category:Aircraft registrations (flat list), I think this is unnecessary, and imho Category:Aircraft registrations by aircraft assigned would be outright confusing. Btw, you created the two latter categories (by registration by manufacturer / by registration by type [model]) last year, so how come you changed your mind now? As I see it, the focus is already on the registration numbers now – even with names like "xxxx (aircraft)". If it's really that common for commercial registrations to be changed, Category:Re-used aircraft registrations with xxxx (specific aircraft) subcategories should become more populated though. Different aircraft should not be lumped into a single registration category. De728631 (talk)
My apologies for not being clear. I don't propose changing the xxxx (aircraft) naming scheme. I do however, think that the meta cats they are in should be renamed per my suggestions above. You are right that some of them are ones I created myself under flawed names. I named them as I did in order to keep with the naming of Category:Aircraft by registration, but I wasn't thrilled by it at the time, and I am even less so now. I'm not sure what you are concerned about with lumping. As it stands now, if a registration is applied to multiple aircraft (which is less common than one aircraft having multiple registrations), then it should be broken down (see Category:N305FA (aircraft)). The main registration category should be also categorized in Category:Re-used aircraft registrations. That is current practice, and I don't think anyone is suggesting changing it. Josh (talk) 21:19, 10 April 2018 (UTC)
Military ID numbers are a problem though. Apparently there are in fact two major approaches among the armed forces of how to apply such registrations, namely using an aircraft's generic serial number (e.g. US Air Force, Italy) or issuing an unrelated ID (Germany, UK, Netherlands, etc.) Sometimes like in Italy or Spain, there are even two parallel schemes of markings on a single aircraft, such as an internal squadron ID (e.g. 41-12) and a permanent serial number. This has already led to inconsistent category schemes as in Category:Military aircraft registered in Spain or Category:Military aircraft registered in Italy (see the MM##### serials). So these need some consistency. De728631 (talk) 09:54, 10 April 2018 (UTC)
The US is no different than Germany or the UK: none use a 'generic' serial number, but instead assign their own numbers per whatever system they have established at the time. Some of these systems adopt the serials already assigned by other agencies or the manufacturer, but again, the sytems are set by each individual issuing authority. What is fundamentally different are identifiers that are assigned for the service life of an aircraft (such as the US Navy's BuNo) vs. those that are assigned to indicate organizational assignment and may be changed throughout its service life (such as the US Navy's tactical codes). However, in all cases, just as with civil registrations, the categories are for the identifier, not the airframe, and thus they should all be handled within the same consistent structure regardless of local differences in how such numbers are devised. Josh (talk) 16:46, 10 April 2018 (UTC)
Thanks for clarifying the service-life ID vs tactical code schemes. It is essentially what I tried to write above but maybe it didn't come through. I agree that in the future we should not use any tactical codes for "registration" categories but stick to BuNos, serials and other such official "top-level" IDs. Where applicable, we should redirect existing "tactical" categories to categories with the official registration number, e.g. Category:43-28 (aircraft)Category:UD.13-28 (aircraft). De728631 (talk) 20:48, 10 April 2018 (UTC)
I totally agree with you that the 'tactical codes' and the like should not be necessarily considered aircraft registrations, while 'serial numbers' like BuNos, etc. should be under aircraft registrations. I also agree that it is curently not consistent and has been hard to know exactly how to proceed with those kinds of categories. We can have 'tactical code' categories, but they should be kept in their own category. The difficulty will be that many users may not be aware of the differences. Josh (talk) 21:19, 10 April 2018 (UTC)
definition of Category:B-6140 (aircraft) is an 'aircraft registration' : now Category:B-6140 (aircraft) does not have any definition. But, for example, Category:Civil aircraft by country, Category:Airliners of Spain, Category:Four-engine airliners, Category:China Southern Airlines have (even human readable, not to mention the machine-readable, as, for example, in Wikidata or Commons' Category:Airbus A380). --Fractaler (talk) 12:17, 11 April 2018 (UTC)
Do you mean that the definition should be reflected in the name of the category? De728631 (talk) 15:09, 11 April 2018 (UTC)
Now on the page Category:B-6140 (aircraft) we can see such static information: Airbus A380-841, cn/serial number: 120, *China Southern Airlines 2013 to date as B-6140. No "is an 'aircraft registration'" on the page. And the pages from the examples have definitions on their pages ("China Southern Airlines is an airline based in Guangzhou in the Guangdong province of the People's Republic of China (PRC)", etc.). --Fractaler (talk) 06:26, 12 April 2018 (UTC)
Or, for example, Wikidata's definitions:

--Fractaler (talk) 13:11, 12 April 2018 (UTC)

Those infoboxes are well suited to gallery pages, but not so much for categories. Wikidata doesn't have items for individual aircraft registrations as far as I am aware. I just looked it up and there are no items with instance of: Q838849 (aircraft registration) Josh (talk) 21:17, 12 April 2018 (UTC)
Do you mean these items? About definition: in order to be able to display the definition (by version of WD, if there is no version of Commons) on a category page, I'm now trying to make a template {{DescriptionWD}} (using Module:Wikidata description). For example, "aircraft registration": registration and identification assigned to an individual aircraft by national aviation authorities --Fractaler (talk) 07:59, 13 April 2018 (UTC)
Try Template:Individual aircraft and Template:Wdd. Josh (talk) 19:07, 13 April 2018 (UTC)
@Fractaler: Yes, none of those items you linked are instances of aircraft registrations. Josh (talk) 19:18, 13 April 2018 (UTC)