[Tagging] layer=-1, rivers, bridges and tunnels

Martin Koppenhoefer dieterdreist at gmail.com
Fri May 2 15:48:52 UTC 2014

2014-05-02 17:23 GMT+02:00 Pieren <pieren3 at gmail.com>:

> On Fri, May 2, 2014 at 4:41 PM, John F. Eldredge <john at jfeldredge.com>
> wrote:
> > Layer = -1 is not valid data for a waterway that is on the surface,
> which by definition is layer 0. It is only valid data on an underground
> waterway.
> Pfff, Martin, why did you restart this thread ?

sorry, came back from holidays and didn't see that is was already a week
old. ;-)

> Water is always below the ground, otherwise it's a flood ;-)

nope, waterways are almost always on the ground  (surface water, french:
eaux superficielles), otherwise it is groundwater (french eau souterraine).
Rivers, streams, canals etc. are generally surface water.

Anyway, this has nothing to do with the layer tag. I believe it was already
said ~5 times this year on this list, but some repetition won't harm:
if no explicit layer tag is set an object is supposed to be on layer=0, but
this has nothing to do with underground vs. on the ground. The layer tags
define stacking locally, i.e. when several objects overlap (in 2D) a
different layer tag indicates that this is not happening in the same layer,
but that one object is above the other, the higher the layer number the
higher the object. Objects at the same spot on the same layer do

This has also nothing to do with tagging for the rendering, it is a rough
representation of 3-dimensional objects in a 2,5D space. When rendering you
can use the layers as rendering order, but you do not have to, often you
will decide to draw lower features above higher ones in order to make them

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