OpenStreetMap

Disused=yes and abandoned=yes

Posted by Andrew Chadwick on 5 June 2011 in English (English)

After several months of sitting on my backside about this, I've decided to try and rehabilitate these two offending little tags. They look so simple in theory, don't they? You just add

disused=yes

to something to mark as it disused, and you're done, right? Wrong, because it generates inconsistencies and internal contradictions in the data if you tag a disused pub, say, like the wiki docs used to recommend:

amenity=pub
disused=yes

Oops. Logically, something can't be both currently used as a pub and currently disused. Additionally, software written without knowledge of the magic "disused=yes" or any of the many other weird and wonderful tags that share the same pattern. Which means that routing engines may route people to disused objects, and disused objects render on the map. This calls for a better approach, a backwards-compatible one: namespaces and better docs to the rescue. For ages now, folks on IRC and mappers generally have been doing something like

disused=yes
disused:amenity=pub

to prevent software that has no reason to understand new magic tagging from doing the wrong thing. I've just written it up at

http://wiki.openstreetmap.org/wiki/Key:disused
http://wiki.openstreetmap.org/wiki/Key:abandoned

with some thoughts about naming and and when a building stops being a building. It's looking good to me, anyway.

In general, tag-semantically, if you're proposing a tag like this which completely breaks the meaning of other tags or keys, you probably shouldn't. But if you want to, please consider a pattern like this to prevent bad data from happening.

Comment from ALE! on 6 June 2011 at 09:10

Thank you for this post! It clearified a lot of things.

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Comment from craigloftus on 6 June 2011 at 09:15

Do you think there is a role for "former", which is in a similar vein to "disused", "abandoned" and "historic?

I've seen and myself used former:* to describe things that used to be there, and are likely to come back again, either with the same properties or similar.

For example, a set of bike racks that have been removed because they're damaged; one expects the council will replace them, but it will probably take ~6 months.

I expect this is covered by "don't tag things that don't exist", but that is a rule that is made to be broken; 'exist' being such a vague and esoteric notion.

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Comment from Andrew Chadwick on 6 June 2011 at 10:26

@craigloftus
Existence seems pretty concrete to me. If you can stub your toe against it, it can be mapped. Unless it's been obliterated and fully wastelandified, that is.

If it's just for other mappers, a note-object with what you expect to come back squirreled away in some namespace is polite. Not sure if it needs documenting really, but you should definitely make the tags non-current somehow.

I don't think we actually -need- a complete life-cycle representation, but we seem to be evolving something like {construction → current → disused → abandoned → historic}. Ick.

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Comment from zmonkey on 7 June 2011 at 05:08

disused railways are tagged 'railway = disused'

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Comment from Vincent de Phily on 7 June 2011 at 13:33

I like this use of a namespace, it's fexible and elegant. Although I'm not very keen on mapping disused features in the first place, this method at least doesn't screw up simple users.

You can also say what feature of the object has become disused : maybe the pub still exists but its website hasn't been updated in 15 years. Maybe you're mapping an antena (man_made=tower) that isn't used for communications anymore. In that context, I think that the plain "disused=yes" tag should not be used at all: only put various keys in the "disused:" namespace but do not add a "disused" tag.

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