On 2012-12-17 22:16, Martin Koppenhoefer wrote :
2012/12/17 A.Pirard.Papou <a.pirard.pa...@gmail.com
<mailto:a.pirard.pa...@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).
Altitude is not height over ground but above sea level.
I am of course speaking of relative altitude.
Position is an improper term as it applied to all directions.
We badly need precision.
. 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.
Agreed. And this is why I said that the tag should be called level.
Transforming that into layers is a renderer's matter that is strictly
forbidden to speak about. Yet...
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?
Exactly as you say above. They are the actual relative levels of these
objects.
I have never seen a bridge sitting on a road (and hiding it, even just
as a hint).
Is there a page in the wiki which encourages this style?
No but their should according to what both of us say about levels.
Respectfully, I have only tagged streams that way because it doesn't
hurt anything and it's superb.
When I don't agree with some way of tagging, I just don't tag.
It's well enough having been accused of badly tagging boundaries when I
only continued tagging the same way they were being tagged and it's done
all over the world I investigated.
Strange thanks. I simply stopped tagging boundaries.
Cheers,
André.
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