[OSM-dev] Polygons in OSM don't necessarily comply to simple feature specification

Karl Newman siliconfiend at gmail.com
Wed Apr 16 22:39:17 BST 2008


On Wed, Apr 16, 2008 at 2:28 PM, Martijn van Exel <mvexel at gmail.com> wrote:

> Hi all,
>
> I've been warming up as many of my colleagues to OSM as possible, and
> sometimes this comes back to me. Being GIS people, they have GIS
> requirements, and OSM was not devised specifically with GIS
> requirements in mind. That said, yesterday a colleague approached me
> asking why OSM data doesn't comply to the Simple Feature
> specification[1] (allowing easy import in for example SQL Server 2008,
> which he was actually attempting). The only exceptions apparently
> being that self-intersecting polygons are allowed in OSM. He found a
> couple hundred in the Netherlands' OSM data.
>
> Is this something that is being considered? I guess it would be easy
> to check for self-intersection upon adding / changing a polygon. Is
> there a specific reason why self-intersecting geometries would be
> explicitly allowed?
>
> Take care,
>
> [1] http://en.wikipedia.org/wiki/Simple_Features
> --
> martijn van exel -+- mvexel at gmail.com -+- http://www.schaaltreinen.nl/
>

I doubt they were "explicitly allowed". Heck, there isn't even a "polygon"
type (although I hear there used to be...) More likely they're just not
explicitly denied. And without an explicit polygon type, they can't be
filtered/denied without determining if it's a polygon or not, which would
involve evaluating the way tags against some (changeable) rules which govern
whether the particular way should be treated as a polygon.

Karl
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