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

Martin Koppenhoefer dieterdreist at gmail.com
Mon Dec 17 21:16:56 GMT 2012

2012/12/17 A.Pirard.Papou <A.Pirard.Papou at gmail.com>

>  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"?)

no, it is not altitude (height over ground), it is the relative position
(relative to other objects at the same spot).

> . 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 is a way to describe in the database which object is above which or
whether they are at the same level.

> 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.

The best way to know what he had in mind would be to write to this person
and ask. As tram rails are (usually) on the same layer/level as the road
itself I'd consider it wrong to have them on different layers.

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.
very strange way of mapping IMHO, how did you come to this idea? Is there a
page in the wiki which encourages this style?

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