[Tagging] site relations for city walls?

Lionel Giard lionel.giard at gmail.com
Tue Jul 14 14:53:13 UTC 2020

> Wouldn't a multipolygon with just two outers solve that parking case?
> Best Peter Elderson

That's a bit of a stretch of the multipolygon definition as there is no
inner ring.  I never used multipolygon for anything else than complex
geometry (with inner ring(s)) and that seems to be what the feature is for.

As we already have the site relation for grouping features that are part of
the same thing, but disjoint, i think that it is good to use it. It also
solves the problem when mappers use multipolygon for two polygons sharing
the same edge (it is forming an invalid geometry), while with site relation
it is not a problem. Another advantage is that it is quite easy to edit.
You just need to add or remove a feature : no specific roles (yet) or order

Le lun. 13 juil. 2020 à 23:29, Volker Schmidt <voschix at gmail.com> a écrit :

> On Mon, 13 Jul 2020 at 22:56, Martin Koppenhoefer <dieterdreist at gmail.com>
> wrote:
>> actually all of these could be „grouped“ with tags alone, e.g distributed
>> museums could have an identifying „network“ tag (or sth similar).
> But why invent a new network tag, if we have  a site relation, waiting to
> be used. (I was thinking of open air museums, where the various exhibits
> are spread over the landscape)
>> For power plants a site might be appropriate, if an area does not do it
>> and you don’t want to rely on only tags.
> If you have ever looked at the complexities of a hydro-power-plant with
> dams, lakes, pipes, turbines deep in the mountains or in dedicated
> buildings . they are really complex, and only parts of it are visible on
> the surface.
>> In theory objects like the Great Wall in China can and should be modeled
>> as areas, although they seem to be linear in nature, they are also thick
>> enough to „require“ an area representation in order to be well mapped in
>> the scale of OpenStreetMap (you can walk on it).
> That's not true - you can walk on parts of it, other parts are completely
> missing, others are heaps of stones.
>> In practice we would also want a way to have preliminary mapping as a
>> line, and mixed geometry relations. A multipolygon relation for all parts
>> of the great wall would likely be broken every day, and would be over the
>> member limits for relations.
> It's not a multipolygon - it is bits and pieces, some connected, same not.
> Some may be linear (in first approximation).
>> Would those that are in favour of using a site relation for a linear,
>> circular, interrupted structure, 19km long and some meters wide, also see
>> it as a good relation type for the Chinese Great Wall?
> You lost me with your question here.
> Volker
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