[Tagging] key damage and HOT

[Paul Allen]

On Thu, 6 Feb 2020 at 05:06, Warin <61sundowner at gmail.com> wrote:

> It seems to me that the present use of the key damage=*, which has no
> documentation, would better fit into the life cycle system.
>

If we need it to map damage all (I think we do) then we need both ways of
doing
it, for the same reasons discussed some weeks ago regarding disused=* and
the disused: lifecycle.

We need both because they have different effects.  They have different
effects because we need those different effects.  I'll use "disused"
rather than "damaged" below to make the point clearer.

Lifecycle prefixes prevent rendering of the feature.  They are equivalent to
deleting the feature tag and adding a note to the effect that the object is
a disused <whatever>.  Except that the word "disused" might not appear
in the note and a synonym or circumlocution might be used instead.  Having
disused:amenity=hospital allows database queries to pick out hospitals
(used or disused), disused hospitals, or functioning hospitals.  Removing
the amenity=hospital tag completely prevents the object appearing in
queries for hospitals, or for disused hospitals.

Having disused=* doesn't prevent rendering.  A disused water tower looks
like a functional water tower and is (usually) a landmark used for
navigation.  Again, database queries can pick out water towers, disused
water towers and functioning water towers.

Is having two ways of doing it tagging for the renderer?  No more than
having
amenity=hospital or removing amenity=hospital.  One renders the object
as a hospital and the other does not: the mapper chooses based upon what
the object is.  Objecting to a mapper being able to decide whether it
is rendered as a hospital or not means objecting to being able to tag
a POI in any meaningful way.

Isn't it recording history and OSM doesn't do that?  It serves two purposes:

1) QA.  A formalized way of telling other mappers that no matter what the
POI looks like in aerial imagery, street-level imagery or a drive-by, the
object
isn't what it appears to be.  A note could do that, but is opaque to
database
queries ("former hospital," "was a hospital," "no longer a hospital," etc.)

2) A formalized way of telling data consumers who query the POI that it
isn't what it appears to be.  Don't hang around that church you spotted and
wait for it to open up so you can have a look around, it's disused.

Will all renderers honour those interpretations?  Probably most will.  It's
easy to not render tags with lifecycle prefixes by simply ignoring them
as being unknown.  It's easy to render tags with disused=* by ignoring
"unknown" tags.  A renderer would need extra code and have to be
somewhat perverse (IMO) to render tags with lifecycle prefixes or
not render POIs with disused=*.  We can probably rely upon these
behaviours for most renderers.

There are two ways of doing it, and ithat's a good thing.
-- 
Paul
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