[Tagging] SF Muni tram lines are layer=1? and general tagging levels considerations

Clay Smalley claysmalley at gmail.com
Mon Dec 17 18:48:51 GMT 2012

On Mon, Dec 17, 2012 at 11:40 AM, A.Pirard.Papou
<A.Pirard.Papou at gmail.com>wrote:
>  A level is an altitude.  A layer is a drawing opacity.  Although OSM does
> not tag for the renderer, it uses the tag *layer=**. It defines *layer*as the relative "position" (is that "altitude"?). In fact, the only effect
> of assigning a layer is that upper layer objects hide lower layer ones
> (it's not a "mind your step" warning ;-))
> It's interesting to keep all the rails in the same layer to avoid splits
> and layer =+1 may be needed for them to show at some places. My reaction
> would be that the person having cared to explicitly set the level might
> have had something on his mind.
It's true that we don't tag for the renderer. My reasoning was that we have
a separate renderer for public transit.

 I have traced lengths of streams
>    - stream as a constant layer=-2 way, uninterrupted end to end (even if
>    they "don't look so deep"),
>     - roads are at level 0
>     - and bridges and culverts at level -1, in the manner mentioned above.
> I've never seen anything tagged like this before. As I've seen it, bridges
are nearly always layer=1 (or some positive number), and the general
consensus on the wiki agrees, so I'm going to keep tagging layers this way.

Also, with your way of tagging layers, how do you deal with a road bridge
that goes over another road?

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