[OSM-talk] Key:layer update

Tobias Knerr osm at tobias-knerr.de
Sun Mar 9 13:00:36 UTC 2014

On 09.03.2014 13:21, Richard Z. wrote:
> the same conceptual problem exists with pylons where they are shared by two bridges
> or aerial tramways. Actualy every pylon breaks the rule by definition because it 
> connects "ground" with layer=0 with something else at a different level.
> How do you want to model such cases better? Lifts in buildings?

Typical pylons aren't a problem because the "ground" is not an OSM
element that they could share a node with. Pylons shared between more
than one bridge are indeed an interesting problem for 3D mapping, but
I'm not aware that this is commonly mapped or used by applications yet,
so there is still some room for establishing good standard practice.

Lifts in buildings don't use layer, they use level. That tag follows
different rules than layer.

> In practice this rule is broken more often than you would think: Hamburg is full
> of waterways connected with roads on bridges through a tag obstacle. France is 
> full of bridges sharing a node with the waterway bellow.

I would prefer correcting these errors instead of changing the rule they

> It may be worth to tag have such a rule restricted for "ways of the same type"
> and a short well defined list of exceptions.

The rule is also needed for ways of different types, e.g. for ordering a
stack of road, railway, and waterway bridges.

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