[OSM-talk] Nested areas

[Dave Stubbs]

On Thu, Jun 5, 2008 at 5:24 PM, Martijn van Oosterhout
<kleptog at gmail.com> wrote:
> On Thu, Jun 5, 2008 at 2:07 PM, Dave Stubbs <osm.list at randomjunk.co.uk> wrote:
>> Layer tags on areas are pure evil. The layer tag is there to indicate
>> vertical separation, not to give a handy z-order hint to the renderer.
>> So unless you do genuinely have two areas which are physically
>> suspended one on top of the other then please don't add layer tags!
>> Thankfully the mapnik maps will just ignore them.
>
> Not entirely. On the NL list we had a building overlapping a water
> area and mapnik was drawing them in the wrong order. Due to the
> shapes, the building covered more area. Perhaps longterm we should
> change the styles to always draw buildings over waterways, but for now
> a layer tags fixes it nicely.
>


It might fix it. But it doesn't fix it nicely.
You're taking something meant to represent a physical property, and
abusing it to produce a pretty map. The question here is whether your
building is actually over the water or not; if it is then adding the
layer tag is actually correct for once, but if it isn't then please,
please invent a new tag rather than abuse an existing one.

Although that's been going on for ages now with the layer tag, so it's
quite possibly useless except as a render hint which is a pity.
At least it's not quite as silly as natural=land.

Dave