[Tagging] How to map terrace buildings with names

[Skyler Hawthorne]

On Tue, 2020-07-07 at 22:14 +0100, Paul Allen wrote:
> Consider a house.  In your understanding it is both a building and a
> house,
> and we tag it building=house.  Now consider another house is built
> adjacent and conjoining, so that they share a side wall.  Two houses
> in your understanding.  If they were both built at the same time by
> the same builder, we could say they were one building.  But
> these were built at different times, in different styles by different
> builders - one building or two?  What if they were built at
> different times by different builders but in the same style so
> they harmonize (without historical data you might think
> they were built at the same time).

My own personal interpretation would be to say that if two houses share
a wall, they are part of the same building. Buildings are expanded all
the time. If a shopping mall expands a wing to give more space for more
shops, we do not say the new section is a separate building; we say the
building has gotten larger.

I said this earlier in the thread, but I think it is still applicable:
when we're tagging shopping centers, where there is a large building
containing several shops, we tag the large structure as
building=retail, and the shops as amenity=*; we do not map them as
building=shop or something like that, because they are not separate
buildings. Why do this for houses/dwellings?

> 
> If there are three houses they are a terrace (maybe) but if there
> are only two houses then they are both semi-detached buildings
> (except few bother with that tag).  We've tried various ways of
> dealing
> with these things.  Reality is messy.  Our tagging is messy.  Sadly,
> these
> are two different messes.
> 
> i see only three cases where I'd use building=terrace
> 
> 1) I want to map a row of houses from aerial imagery where I don't
> know the addresses and can't precisely determine the boundaries so
> don't even know how many dwellings there are.  I tend to avoid
> mapping this type of situation.
> 
> 2) The terrace itself has a name that is a required part of the
> address.
> This is a horrible situation, not well-handled by any solution. 
> Especially
> when some of those houses may have their own names.
> 

Your personal justificatons for your mapping choices are perfectly
fine, but that's not what I'm proposing changing. Since it is not well-
defined what to do when a terrace has a name, that is why I am
proposing the tagging scheme with a different usage of building=terrace
than what you and the wiki say, that is, only when you don't know the
borders of the individual dwellings. We can choose to expand its usage,
and I don't see why not to. It does not introduce any new tags, or
propose changing any existing map data, and it fills a gap for certain
use cases.

> 3) The terrace has a name which is no longer part of the address.
> It is at one end of what is a very long terrace of houses built at
> various times and which share side walls.  The fact that five
> houses were once referred to as Priory Terrace in times long
> pass didn't merit wrapping them in a building=terrace.

I think it's well-understood that OSM should prefer the present reality
on the ground. Historical names and other data aren't under discsussion
right now.

-- 
Skyler