[OSM-dev] Coastlines and water - contact and technical

[Ben Supnik]

Hi Jon,

Jon Burgess wrote:

> I believe (a). The wiki documentation for multipolgons has two slightly
> contradictory recommendations:

Yeah - I just stumbled upon that...given the discussion it certainly 
seems like tagging the relation is better than tagging the way...

- If we have a multipolygon, understanding the way without the relation 
and sibbling ways is going to be impossible (that is, the results will 
be spatially incorrect) in all but a very few cases.  So I think clients 
need to be multipoylgon aware.

- Better to have the tags on the relation and not have any issues of 
ambiguity.  Tagging the underlying ways seems like a way to get 
inconsistent data.

> That would be a good thing to do. Sometimes there is more than one way
> to tag something and this does not necessarily mean that one of them is
> incorrect.

I will try to output a list of problems as I process the file.

> If however the relation was also tagged, perhaps with a boundary tag
> describing the name of the region then it would ignore the tags on the
> ways.

Does pgsql exclude the way as a way-area due to its membership in a 
multipolygon relation?

What I mean by this is: I have a closed way with landuse=water, which is 
a lake in its own right.

I then put it in a multipolygon relation.

If I understand correctly, the lake from a single way is an "area" and 
can be parsed as such...its area would then be re-processed when we 
handle the multipolygon, which might have different tags.

Or do data interpreting clients have to recognize the way in the 
relation and exclude its interpretation as an area?  This seems like an 
inconsistent thing to do, particularly since holes can be areas in their 
own right.

cheres
ben

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