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I'm thinking of proposing a new feature, which I haven't found a reference to on OSM wiki.

The proposal concerns minor buildings on a residential property - sheds, garages, playhouses, etc. There does already exist well established tags for specific building functions, like building=shed and building=garage. However it's often difficult to reliably discern the function of a small building from the aerial imagery. Rather than spending time to analyze the image, and making a guess of what the building is, it'd be more useful just to tag what's realiably known from the image. And what's clearly known is that they are less significant buildings than the main house on the same property, no matter whatever their actual function happens to be.

So, tagging these minor buildings differently from the "major" buildings would be useful, even in cases where it's not known what exact type that minor building is. For example that information could be potentially be used in rendering, drawing such buildings as bit less prominent, like building=house are currently less prominent compared to the generic building=yes. (I realize rendering changes are unlikely to happen, but I'm talking in principle here.)

My question concerns whether it would be better to:

1) propose a very general purpose tag, such as "building=minor" that could be used refer to any building that is always conceptually in relation to a "main" building of a site, but of significantly minor significance. This could then be used in any context where one building is the prominent one, e.g. with a factory that has minor buildings (of unknown function, maybe storage) nearby.

2) propose a more specific tag for the purpose, such as "building=residential_property" or "building=residential_minor"

3) not propose any new tag, but rather just use building=residential, even though that doesn't convey the minor significance of the building. (To show the difference: building=residential could just as well be used to tag the main house on the property, but the new building=minor could not bo (correctly) used to tag that.)

I'm inclined to think the first option would be best.

The only reference to such a feature I've found is a question on this forum: "How to tag residential properties garages, sheds etc?" I haven't found any similar feature in use from taginfo.

(And yes, I realize because of the wiki nature I can start using pretty much any tag I want without proposing them, but I wanted to ask which more experienced mappers would consider to be the best approach in this case.)

asked 07 Feb '12, 06:26

Ilari's gravatar image

accept rate: 0%

edited 07 Feb '12, 12:14

The general idea is that the building is tagged building=yes because the mapper has identified a feature on the imagery that conforms to that of a structure of unknown usage. Once you start tagging a feature as something more specific such as shed or outhouse then subsequent mappers assume that tag is there because someone has identified that structure and knows it's use and has classified it as such. In your suggestion this is not the case, you want to "guess" the status of the structure without factual or local knowledge and this would be misleading to subsequent mappers. A smaller structure on a residential property could be a garage ...but could just as easily be a garage converted to a granny flat. A large structure tagged building=yes and a cluster of smaller structures around it also tagged buildings=yes will speak for itself without conveying any specific usage of those structures. The intelligent algorithm will have been designed around local averages (i.e. a residence consists of one main building, one garage, one/two/three "other" usage buildings, and may even have an addition of say 1 in 5 may have a granny flat) so while size does matter, guessing does not.

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answered 26 May '15, 08:37

RAytoun's gravatar image

accept rate: 0%

good point about unusual not minor usages only visible locally and not from satellite images. But this only applies to building:use= as building= is the purpose the building was originally build for, which would still be e.g. a garage, even if it's now used as a flat.

(24 Aug '18, 00:43) hackthemap

In some countries, these minor residential builidings are collectively known as "out buildings". One solution for these unidentified "minor residential buildings" is to create a new tag scheme: building=out_building out_building=shed/garage/playhouse/gazebo/*

alternatively, use building=out_building when the type is unknown and building=shed/garage/playhouse/gazebo/* when it is known.

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answered 23 Sep '13, 06:46

rovingmedic's gravatar image

accept rate: 5%

Wouldn't the same be achieved if building=* is set to shed/garage etc. when the detail of the outbuilding is known? Grouping building types as not important / out buildings in the rendering should not be the problem.

(24 Aug '18, 00:45) hackthemap

If you do not have enough information to tell what kind of building it is but still "know" that it's a "minor" building then how do you know it ?

My guess is that 99% of the time you know because that building is smaller than the nearby ones. If building size is your source of information, then you might as well not do any "vague tagging" and let the renderer/analyzer use the already-available size information directly ?

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answered 07 Feb '12, 13:32

Vincent%20de%20Phily's gravatar image

Vincent de P... ♦
accept rate: 19%


True that using relative building size could be a good guide point for automatic rendering. However, there is some furhter (instinctive) human analysis that goes into it - e.g. the placement, type of paths leading to the structure, length of it's shadow, texture/condition of the roof. As an analogy, you could just as well say it's useless to tag building=house, just let the renderer determine it by treating largest buildings in a residential area as houses.

(07 Feb '12, 13:41) Ilari

Further, in my experience while it's effortless and absolutely clear for a human to say something like "why, that's cleary the smaller building", once you try to put that same logic to an algorithm, mistakes start to appear. Also, in my (admittedly limited) knowledge, having the renderer do auto-analysis in this way isn't very consistent in the way that OSM works.

(07 Feb '12, 13:47) Ilari

Yes, an algorythm would make mistakes. But so would a human (since we're talking about buildings that are hard to identify to begin with). How much better I dont know...

But I'm beginning to think the point is moot : if the data you're about to put in is that vague and unreliable, you might as well leave it out. A human looking at the map will probably figure as much anyway, and lookup the imagery if in doubt. A program looking at the data would probably trust his own (size/layout-based) algorythm.

(07 Feb '12, 22:12) Vincent de P... ♦

You mention taginfo, which already has over 3000 building=shed, over 155,000 building=garage (and over 72,000 building=garages). Garage and garages already render less prominently (as building=house and building=residential do). If you want building=shed to render similarly then I think trac is the place to request it.

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answered 07 Feb '12, 07:18

EdLoach's gravatar image

EdLoach ♦
accept rate: 22%


No, you misunderstand me. The point is I don't want to try to guess whether they are sheds, garages, playhouses, covered garbage bins other such structures - the only information that I can reliably tag from the aerial images is that they are less significant structures than the nearby house. I'll revise my question to reflect this.

(07 Feb '12, 11:47) Ilari

I now revised the question in hopes it's more understandable. I also added a third "option" of doing nothing, though I clearly don't think it's a good one. :)

(07 Feb '12, 12:03) Ilari

Hmm, this seems to be gaining upvotes even after I've explained the misunderstanding. Maybe I'm the one who doesn't understand? Could someone explain further how this resolves the situation where I cannot reliably determine whether a structure is a shed, garage or neither?

(07 Feb '12, 14:33) Ilari

If you can't tell from imagery, tag it building=yes and do an on the ground survey (which is what I use building=yes for - buildings I don't know enough detail about to tag them as anything else).

(07 Feb '12, 14:39) EdLoach ♦

@EdLoach But building=yes does not contain the information that could be used for rendering it properly (quite the contrary, if there are building=yes near building=house, the minor buildings render more prominently). And ground survey isn't very practical in all cases, and even when it is if all that I'm getting out of it is whether a small building is a shed or a playhouse, I don't (personally) see how that's worth the effort, since it'd be possible to convey the relevant information ("this isn't a very important building") in other methods.

(07 Feb '12, 19:29) Ilari

I think this query has some merit and should result in a debate on the proposed features page. What I would suggest, however, is something like this:

Keep building:yes as the main tag and allow:









It is as you say a wiki and if someone wants such detail in the area of his/her interest then so be it. Such detail could be rendered "as you like it" whereby the general mapnik renderer would stay the same. Or something like that!

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answered 07 Feb '12, 06:41

dcp's gravatar image

accept rate: 0%

edited 07 Feb '12, 06:44

The question is about minor buildings on a residential property.

(07 Feb '12, 11:03) Pieren

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question asked: 07 Feb '12, 06:26

question was seen: 11,631 times

last updated: 24 Aug '18, 00:47

NOTICE: is no longer in use from 1st March 2024. Please use the OpenStreetMap Community Forum