[OSM-talk] Underground / hovering buildings

Nathan Edgars II neroute2 at gmail.com
Tue Feb 15 22:11:16 GMT 2011

Jacek Konieczny wrote:
> layer=-1 tells only that the thing is under layer=0 and over layer=-2,
> nothing in relation to 'ground level' (some rivers or roads may have
> layer=-1 or layer=1 on most of its length).
No, ground level is layer 0. A nonzero layer on a ground-level feature is an

However, layer=-1 does not mean it's covered by surface, if the surface has
been removed. For example, during construction of a building, the basement
will be open to the air.

For the original question, I'd probably use layer=-1, covered=yes,
underground=yes, location=underground, and enough other semi-made-up tags
that one is bound to stick.

In addition, it's not always clear what ground level is in dense urban
environments. In part of downtown Chicago, the pre-civilization ground level
is now under two levels of elevated streets. But there are buildings that
fill the formerly-open spaces, so in some sense ground level has moved up
two layers. Here it's probably best to explicitly label layer=0 on
whatever's chosen as the current ground level.
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