Allow "layer" tags alone to resolve building crossing issues

[quincylvania]

Closes #5924.

This lets instances of buildings crossing highway/railways/waterways to be disambiguated by simply setting different layer tags. The covered tag is ignored altogether.

Leaving this as a draft since I'm still not 100% sure this is the desired behavior.

This also makes makes the Layer editor visible in the Structure field even without a structure tag if a "layer" tag is present

[BjornRasmussen]

Thanks for this!! The JOSM validator currently works like this, so this will be nice to avoid confusion about the validator

[bhousel]

I'm wary of this approach, because I still think the ground has an implied layer 0, and features below it may not render.

[BjornRasmussen]

I agree with @bhousel - we need to make sure that, for example, a service road under a roof doesn't get the tag layer=-1

[cserpell]

Please make this through, this issue is driving me nuts with some new editors that do not understand that adding the layer=1 to a building=roof (specially in gas stations) is enough to make all service ways below to be ok.

[kymckay]

@cserpell According to the layer tag wiki page this is not true

When ways are passing on different levels apply layer=* only to the way which also has the bridge/tunnel attribute. Only ways with one of the tags/attributes tunnel=, bridge=, highway=steps, highway=elevator, covered=* should be tagged with the layer tag, similar for railways and waterways.

I'm not sure where steps and elevators come into it, but this matches my understanding of the layer tag. The feature still must be tagged appropriately

[matkoniecz]

Fortunately negative layer does not mean that something is underground, explicit location=underground should be used to tag this.

[quincylvania]

Does this approach (not requiring covered=yes) sound okay if iD wouldn't assign negative layers?

[bhousel]

If you want to hard-code rules for roofs, go ahead.

[quincylvania]

If you want to hard-code rules for roofs, go ahead.

I don't particularly. But I think if any building has layer=1 with a crossing road then it's implied that the building covers the road and iD shouldn't flag it.