[Talk-us] script for adding layer=1 to bridges

Anthony osm at inbox.org
Thu Jan 28 23:35:40 GMT 2010

On Thu, Jan 28, 2010 at 6:14 PM, Dale Puch <dale.puch at gmail.com> wrote:

> Looking at http://wiki.openstreetmap.org/wiki/Layer My take is that the
> open to the air surface is layer 0  Ground or water.

That seems to be the intention, but it doesn't always work in the real
world, mainly because the surface of the earth isn't level.  There's also
the fact that the layer tag is used on ways, and not nodes, and the ways
themselves are often not level.  This latter point usually doesn't matter,
but sometimes it does.

Additionally, I'm not so sure "open to the air surface" is an adequate
definition.  A tunnel is generally "open to the air surface".

So a bridge over a river or dug ditch is layer 1, and the water would be 0

What about a dug ditch without a bridge over it?  Is that layer=0?  It's
certainly "open to the air surface", isn't it?  So when the ditch is dug,
the layer is 0, but then when I stick a plank on top of it it suddenly
becomes layer=-1?

It seems to me that there are lots of situations where the layer tag just
doesn't work.

I feel a script applying layer=1 to any bridge without a layer tag should be
> ok IF it also checks for bridges that cross it and increment those layer
> numbers.

Maybe.  Is a bridge the only way that can be above a bridge?  (Besides
buildings, which cause their own unique problems, anyway.)
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