[Tagging] How to map terrace buildings with names

Skyler Hawthorne osm at dead10ck.com
Tue Jul 7 21:39:53 UTC 2020

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.


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