[OSM-talk] Layers query

Robert Hart Robert.Hart at BuroHappold.com
Mon Oct 9 10:07:14 BST 2006


> >Would it be a sensible convention to use negative values if the way goes
> >underground, and positive if the way goes over a ground-level feature? 

It's not always clear what ground-level is. For example, when a road is on
made-ground they are effectively at ground-level, however other roads
passing under them are also at their own ground level. When does a bridge
become a tunnel? 

> There is an argument to say that the footbridges and underpasses should be
> tagged with some sort of relative elevation tag, whereas areas inside
> areas
> would be tagged with a display order tag (layers is ok).
> 
> Is a distinction between these two logical differences necessary, or not?

I believe so. I'm thinking of those "driver's eye view" maps that navigation
devices use. Roads that pass over or under the current road could be shown
elevated, but I don't think we'd want islands inside lakes floating off into
space....


Rob



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