[OSM-talk] Mapnik handling of highways that are also landuse...

[Dave Stubbs]

On Thu, Aug 28, 2008 at 11:06 AM, Dermot McNally <dermotm at gmail.com> wrote:
> 2008/8/28 Steve Chilton <S.L.Chilton at mdx.ac.uk>:
>
>> There are two reasons why your "tag combination ought to be able to
>> render correctly as is" statement is not valid.
>
> This is always a risk :)
>
>> Firstly - as Thomas pointed out - mapnik likes one feature per way.
>> Secondly - landuse=grass is not rendered at the moment (because of the
>> vast disagreement on the whole landuse/natural/grass thing).
>
> A further complexity, certainly. The amusing thing is, I only started
> using landuse=grass very recently, after deciding that
> recreation_ground was probably not a good tag for what we're
> describing here.



>
>> What I am guessing you have on the ground is a residential square with a
>> road round the outside and a grassy bit in the middle.
>
> Correct.
>
>> There is no way I
>> know of for mapnik to interpret this correctly from a double-tagged
>> single way like this. It would have to be able to draw a line, a road
>> fill, a second line, and then the grass fill.
>> Where these occur in areas I have seen (many grass filled squares in C
>> London) two parallel ways have been used - and yes I know that people
>> are using leisure=park "incorrectly" in order to get them rendered, but
>> probably excusable in London as they are often formal park/recreation
>> areas.
>
> Well, a technical limitation is just that - if it can't be done, we
> need to live with it. The end result is certainly unintuitive, though,
> since the only area tag named (the landuse) isn't the style that gets
> applied to the area.
>

Well, technically, there are ways of handling this case (the way would
need duplicating on import, with some clever tag stripping). But they
aren't pretty, or I think, desirable.

The weirdness is caused by the fact that you have a way which is both
a line and a polygon at the same time, as well as being a road and
grass at the same time. This kind of duality might be OK for photons,
but I'm not sure it makes much sense for data modelling. And if OSM
ever gets a native area type like people keep suggesting, then it
probably just wouldn't be allowed.
There's an easy fix though: just make a 2nd way using the same nodes..
have one be the road, and one the grass.

Dave