Marking that building is gone, but visible on aerials - how to distinguish fully gone ones and cases where ruins remain?

It is well established that buildings that are gone and unlikely to be mapped by accident should not be mapped (use OHM for that)

It is well established that buildings that are gone and likely to be mapped by accident can be mapped with say demolished:building= destroyed:building= razed:building=

But how can we distinguish cases where building is gone and all traces are gone and case where building is torn down but ruins remain?

Maybe if these are used then it express case of building and any ruins being gone? At least typically? And should not be used if ruins are present?

And if ruins are present then ruins:building=yes or similar should be used?

Or maybe demolished:building= destroyed:building= razed:building= are not specifying whether ruins are present and ideally we would have more clear value specifying “no ruins or traces here”?

Or maybe “are ruins here” is not important and worth caring about?

(I am asking as I was working on User:Mateusz Konieczny/ruined building - OpenStreetMap Wiki and I am trying to align it with how people view this tags)

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You may have noticed that @vectorial8192 started a very similar thread about buildings undergoing demolition (for years, as they pointed out in an update).

I have no clear answers or perspectives to these questions. My initial take is that it might often be very difficult to differentiate clearly between simply abandoned buildings, buildings that are in ‘ruins’, and buildings undergoing demolition (for years, or at least for a very long time). Perhaps @vectorial8192 and you could hash out something together, as you seem to be interested in similar cases (so I’m pinging them to this thread too with the @ marker)!

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There is definitely a need for a way to tag buildings that are beyond abandoned (i.e. they are not actively being demolished but slowly disintegrating due to neglect) but do not have historic value so don’t fit historic=ruins. I guess many ruins tagged with the later are so because that’s what turns up when you type “ruin” in iD even though they don’t have historic value. It would be more correct to tag these ruins with ruined:building=* Maybe the border line between abandoned and ruined could be that abandoned buildings still have a roof (though it may be leaking) while ruined buildings have no roof left but may still have walls standing.

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note that “historic=ruins is for objects with historic value only” may be idea that is not generally supported

note that “historic=ruins is for objects with historic value only” may be idea that is not generally supported

How would we be quantifying historic value? IMHO it depends on the context / question that you have, whether a specific relict can be of value or worthless.

Hi all!

Yeah, it seems quite some OSM mappers may think building demolition is “almost always” a quick process (e.g. short building quick job, tall building use “controlled explosion” demolition) so the intermediary statuses can be safely ignored. Well, consider Hong Kong with its insane density, but also a need to rebuild somewhat tall buildings. “Controlled explosion” demolition is basically forbidden, so construction companies had to tear down the building, one level at the time, which is obviously slow.

Which led me to the original “building under demolition” question.

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Anyways, it’s a good idea to list out what we have right now regarding building tagging (or at least what I think we may/should have).

Every building “starts off” as some sort of unused land. Then, as construction begins, someone would add landuse=construction and building=construciton, that kind of stuff. When the building finishes, someone else retags building=yes, or more specific values from construction=???. Simple stuff.

Now if the building is being continuously maintained, we don’t have to worry about it.

The problem is when buildings are no longer continuously maintained, and that’s what brings us here. It seems to me those destroyed/razed/demolished tagging is quite subjective since they also describe the method with which the building is unexisted, and opens up attacks from mappers to dispute the unexistence method, therefore the “validity”/“accuracy” of such tags.

I’m gonna think about this for a while first and then continue typing.

So basically we have the following cases:

  • Abandoned
  • Disused
  • Ruined
  • Under Demolition <----- I am here
  • “Gone”

I’m gonna just type out my thoughts here.

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Abandoned: building is effectively “unclaimed”. Depending on the state of the building, it may be dangerous to get inside, but trespassers are unlikely to be sued.

Disused: similar to “abandoned”, but building is still “claimed” (e.g. security guards standing by at its entrances); as such, trespassers are gonna get sued. I don’t know why this situation exists (especially in Hong Kong with insane land demand), but some examples from Hong Kong:

Ruined: an extension of “abandoned”. Building is obviously damaged (the method does not matter; could be from wars/conflicts, could be “natural reclamation”, etc), and it’s unlikely to be repaired any time soon.

  • Avoid creating a damaged=yes tag:
    • Some buildings can appear damaged due to negligent maintenance but are otherwise perfectly usable and structurally sound
    • It is subjective what it means by “damaged”
    • Best correctness would require referencing the original blueprints, but that’s probably impossible

“Under Demolition”: an extension of “disused”. Someone has to claim the building first before deconstructing it. There’s usually a construction area alongside the building. I personally use building=construction + construction=demolition.

“Gone”: building is gone from IRL observation:

  • Method of unexistence does not matter (eg demolished orderly, destroyed by pure chance, razed by bulldozers, etc)
    • Could this be a subtag?
  • If still seen from satellite imagery, add building=demolished / demolished:building=yes (?)

One problem with satellite imagery: a provider may show “gone” while another provider may show “still exists/under demolition”. Perhaps that’s the source of rage/confusion around “remapping gone features”.

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That’s my thoughts on building classification.

definitely the second one, building=demolished / building=collapsed etc are nasty trap for data consumers

seems likely, but I would avoid making it part of definition as in at least some cases it will be different (for example, building may be guarded/unguarded for different reasons)

I recently went through the “long tail” of building values somewhat local to me and classified the ones that are either “not buildings” or “not really buildings”. See “almost buildings” and below here.

I also fixed lots of obvious typos to building types where it was obvious what the original mapper had meant.i

I think that’s a really neat template for classification! Thanks!

The only nitpick I have is that although “ruined” is often an extension of “abandoned”, and “under demolition” often an extension of “disused” (as you wrote), these aren’t strict inheritances. Abandoned buildings can be re-acquired for demolition, and disused buildings can also turn into ruins. Or put more precisely, disused buildings can often be abandoned, and then demolished or ruined.

You write that ruined buildings have to exhibit obvious damage (regardless of its etiology) but that tagging the damage isn’t reasonable because ‘damage’ is subjective. Furthermore you point out that some cosmetically damaged buildings still maintain structural integrity.

I agree on both points, and I think this distinction could be used for demarcating demolition too! The way I understand the process is that before a building is demolished, it is usually vacated and stripped of valuable and easily removed features. Like furniture, electric wiring, and even many non-load-bearing structures—including inner walls or even the facade or outer cladding. During this (perhaps lengthy) time, I’d think, the building isn’t “demolished”, but merely “disused”. The reason being precisely that this equates perfectly to ‘damage’ any “abandoned” of “disused” building might have.

Actual demolition—as I understand the word and process—starts from the time load-bearing structures are being intentionally destroyed to the point when the building is reduced to a heap of rubble (no matter how large[1]). The timeframe of this process varies massively. In explosive demolition, this phase lasts mere seconds. Smaller buildings can be bulldozed in days, and even multi-story reinforced-concrete buildings can be jackhammered to a pile of rubble in a few weeks. Thank you for noting that there really exist some buildings where this process takes multiple months to a year!

As @Mateusz_Konieczny noted, this is precisely the rationale expressed in the Wiki on the demolished: prefix.


  1. Clearing and processing this heap can also take a long time, but since it is a heap and not a building, this isn’t part of the demolition ↩

Now if the building is being continuously maintained, we don’t have to worry about it.

The problem is when buildings are no longer continuously maintained, and that’s what brings us here.

as your Hong Kong example illustrates, it is not simple as that. Buildings also get rebuilt if their operation is less economically beneficial than rebuilding something different (in terms of quantity, energy consumption, spatial structure etc.)

Abandoned: building is effectively “unclaimed”. Depending on the state of the building, it may be dangerous to get inside, but trespassers are unlikely to be sued.

Disused: similar to “abandoned”, but building is still “claimed” (e.g. security guards standing by at its entrances); as such, trespassers are gonna get sued.

I think it is improbable to find “unclaimed” buildings, every building on private land is part of the ground it stands on, which has registered owners (in most parts of the world I guess), there might be owners that are not currently interested in their property (e.g. they have different properties, are old and nobody from their family is interested, are far away, in hospital or in prison, etc.), but it is not a criterion I have heard before in the osm context, the difference between abandoned and disused which we typically apply in OpenStreetMap is about the state of maintenance, disused means good usable state requiring at most minor repairs, while abandoned means more serious damage while probably still recoverable (it is still there but looks somehow broken and deteriorated)

Buildings also get rebuilt if their operation is less economically beneficial than rebuilding something different (in terms of quantity, energy consumption, spatial structure etc.)

I have no idea which example you are talking about, and therefore do not understand what you are saying. If you are trying to refer to this Way: â€ȘPublic Housing Development at Sui Fai Factory Estate‬ (â€Ș237758277‬) | OpenStreetMap , then I must tell you this is a government action on a government property, as part of a (long time?) political agenda to build more housing. It has nothing to do with being economical or not. In fact, one may argue this rebuilding action is uneconomical when the fact was that there were still some commercial businesses inside that Factory Estate before the rebuilding.

Re unclaimed/recoverable buildings, I can see a problem.

Consider a building which is essentially “left to rot”, so nature has decided to eg grow vines around the building. Even with this, the building is still standing. Would this be considered “need minor repairs”?

Another example from Hong Kong: Way: â€ȘMaykong Godown‬ (â€Ș366425151‬) | OpenStreetMap ; they even got trees growing on them, but the structure itself is apparently still sound.

Would this be disused or abandoned? I would tend to tag this as abandoned: they do not have security guards there, and have made no attempts to repair it, so it is essentially “unclaimed”. Therefore, abandoned.

Above examples of disused are cases where the property owner cares little, but still cares, so they install some security guards at those property while still letting those buildings “rot”. That’s significant because those guards are on payrolls. Therefore, disused.