[OSM-talk] Indiscrimate layering

D Tucny d at tucny.com
Sat Dec 20 18:19:53 GMT 2008


2008/12/21 Sven Rautenberg <sven at rtbg.de>

> Elena of Valhalla schrieb:
> > On Sat, Dec 20, 2008 at 1:17 AM, Sven Rautenberg <sven at rtbg.de> wrote:
> >> Please reconsider.
> >>
> >> I hate it when I see rivers, streams etc. illogically marked as
> >> layer=-1. There is no reason to do so, because a river usually is at the
> >> top of the surface, and that is "no layer" or "layer=0".
> >
> > not so true everywhere: in mountain areas rivers are usually at the
> > bottom of valleys,
>
> The bottom of a valley is layer=0.
>
> > and I've seen many small rivers covered and
> > practically brought underground in urban areas.
>
> These streams should be tagged tunnel=yes, layer=-1.
>
> > as a guideline, i usually mark the road +1 if it rises to become a
> > bridge, but 0 and the river -1 if the river is lower than the ground
> > where most of the road is
>
> If you come across an existing stream which has no layer tag, do you add
> "layer=-1" to the whole stream and then check the whole stream if your
> change may conflict e.g. with a tunnel which is already at layer=-1? I
> don't think so.
>
> Tagging a part of a way with a non-default layer does not mean anything
> about it's elevation. It is all relative, but it is a good idea to
> assume "natural surface level" to be layer=0 in most cases.
>
> The stream therefore is the natural surface wherever its water flows.
> The bridge is above the water, so it is layer=1. And it is less
> dangerous when just tagging the bridge compared to tagging the whole
> stream.
>

I also tag many waterways around here as layer=-1, because that's what they
are... thank god they aren't layer=0 or the place would be under water! The
waterways are below the surrounding land, hence the water stays in them,
below the surrounding land... the roads stay on the surround land hence they
stay dry, except when it rains, but...

I will note that around here there are 100s of manmade waterways with roads
passing over most of them with no obvious bridges and no increase in
elevation... There are no instances of roads going under these waterways,
which helps... Where there is an obvious bridge, it is tagged as such...

Layers, like speed, are relative with 0 being default and as such, normal...
so... I personally agree with David and Elena above... If you've mapping
something that is mostly below the majority of other features, make it -1,
if it's mostly above, make it +1, or whichever valid value you choose... For
me... the main road network is layer 0 with anything running over it as a
positive and anything running under it a negative...

d
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