[Tagging] layer=-1, rivers, bridges and tunnels
frankosm at xs4all.nl
Sat Mar 15 16:39:12 UTC 2014
Fernando Trebien wrote:
> Alright. I see that "applying layer to long ways" is bad for several
> reasons. Surely this could be turned into a validation warning.
> But what's the difference between tagging the bridge with layer=1 and
> tagging the river underneath with layer=-1? Some people seem to think
> that both are necessary, many think it's best to use layer=1 on the
> bridge, I'm saying that layer=-1 on the river (let's say a short
> section, not the entire length) is "equivalent". Is it not equivalent?
> Is it wrong? If it is wrong, why is it wrong?
I don't think 'wrong' is the way to approach this; afaik, they are indeed
There are four alternatives which mappers follow, none of which are 'wrong':
tag the bridge segment, tag the water segment under the bridge, tag both, tag
I've run waterway=stream or =canal (or =ditch, I think) through a few of the
small rivers and streams here in the Netherlands. Roads need splitting to make
bridges, so it makes sense to do all the relevant tagging on the road segment
with the bridge tag when you are working on it.
I don't have any reason to split the waterway=*, so I just draw on without
stopping. Since I put the name on the waterway and not on the riverbank, it
leaves it to the renderer to find a good place to fit in the
river/stream/canal name. In principle, that should mean a cleaner map if the
renderer can work out the proper placement (difficult job, though).
So I would be against splitting the waterway at a bridge and tagging it
layer=-1 on practical grounds. And you can be sure that it would cause
confusion with other mappers who would imagine that you are trying to model an
inverted siphon with the piece of waterway tagged layer=-1, or that you had
simply made a mistake. (The 'level' confusion again.)
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