[OSM-talk] Indiscrimate layering

[Sven Rautenberg]

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.

Regards,
Sven