[Tagging] tagging of "ele" / elevation data e.g. in the context of towers

Tobias Knerr osm at tobias-knerr.de
Mon Feb 20 13:15:27 GMT 2012

Martin Koppenhoefer wrote:
> a) ele is the elevation of the ground around/below the tower (in the
> case of a mountain summit it would be the elevation of the mountain,
> not the tower).

In practice, this is closest to how I would have interpreted it.

I would usually expect ele to define the elevation of the "base" of the 
feature that carries the tag. If an object stands on the ground, then 
this is identical to the elevation of the ground at that point.
But in the case of e.g. a tunnel, it would refer to the surface of the 
road running through the tunnel - and therefore an elevation below the 
"ground" elevation. The road running on top of the hill would have 
different ele values than the tunnel running through it.

So no, ele is imo not the elevation of the ground, it is the elevation 
of _the object mapped with the ele tag_. However, in the case of a 
building, that building's elevation is given at ground level.
As a result, the ele tags on features on the ground will be the same as 
ground ele. The ele tags on features above or below the ground, such as 
bridges or tunnels, will be different from ground ele, though.


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