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

Anthony osm at inbox.org
Fri Jan 29 05:02:26 GMT 2010

On Thu, Jan 28, 2010 at 10:13 PM, Alan Mintz
<Alan_Mintz+OSM at earthlink.net<Alan_Mintz%2BOSM at earthlink.net>
> wrote:

> Columbus Blvd is more puzzling. It may be layer=-1 through this whole area,
> or the whole waterfront may be lower than the street level is to the west of
> I-95. This is where I think a local survey of the actual elevations, and
> tagging of layers by absolute levels of elevation makes sense.

I-95 in that area (before, within, and after the "tunnel") is built in a
trench.  I don't think that means it should all be at layer=-1 though.

Tagging of layers by absolute levels of elevation would be great, except for
the fact that "absolute levels of elevation" can be extremely hard to come
by.  Some sort of "relative levels of elevation" would probably be easier.
Break the problem up into two parts and let people work on the two parts
independently.  1) Choose a "surface level" for all points on the earth and
tag node heights relative to that surface.  2) Figure out, for all points of
earth, where that "surface level" lies with respect to one or more datums.

Part 2 (which I picture as http://en.wikipedia.org/wiki/File:Geoida.svg) is
cool, but probably isn't going to interest a lot of OSMers who would,
nonetheless, be interested in mapping part 1.
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