[OSM-dev] Advice sought on polygon-with-hole drawing

Karl Newman siliconfiend at gmail.com
Fri Mar 14 05:10:27 GMT 2008


On Thu, Mar 13, 2008 at 6:15 PM, Frederik Ramm <frederik at remote.org> wrote:

> Hi,
>
> > If I understand this correctly, then for a forested island in a lake
> you'd
> > need to have the island twice in the osm data. Once for the hole in the
> lake
> > and once for the forest on the island.
>
> No.
>
> Assuming for a moment that you really wanted to model the forest as a
> "hole in the island", which doesn't make a lot of sense to me since I
> don't generally map forests as holes in the country, but I understand
> it's only a example, then the island would be there only once, be part
> of two relations, one where it would play the "outer" role to the
> forest and one where it would play the "inner" role to the lake.
>
> Bye
> Frederik
>

I don't think he means a hole in the island. The island itself is just a
simple, single polygon. I think his question is: Can the way which
represents the island also be tagged with a forest which covers the entire
island? In your original pseudocode, the forest bit would be ignored because
only the lake tags would count. I don't see why you'd want to create yet
another multipolygon relation with only one role (an "outer") as you've
described.

Karl
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