I thought levels are just relative to one another. So we just need to indicate which "way" is above the other. This could be with numbers 1000 and 1001 as well as 0 and 1 or -2 and 5.
It's just by convention that tunnels are typically mapped as -1 (except for building_passages under houses) and bridges as 1 (or 2, ... when there are multiple bridges). For me they have nothing to do with ground level. regards m On Tue, Jan 26, 2016 at 11:53 PM, Warin <61sundow...@gmail.com> wrote: > On 27/01/2016 8:50 AM, Clifford Snow wrote: > > > On Tue, Jan 26, 2016 at 1:14 PM, Warin <61sundow...@gmail.com> wrote: >> >> layer=-1 to me says this is below natural ground level. And here that is >> not the case - the road is above natural ground level and that should be >> tagged layer=1 .. to be absolutely technically correct. >> >> But many use the layer=-1 on culverts as a convenience of less work. >> >>>> tunnel=building_passage >>> >>> I am not understanding where that tag would be applied. What would be >>> tagged this way? >> >> >> The convention it to tag what is inside the tunnel. Similar to a bridge >> where what is on the bridge carries the tag. > > > According to the wiki: > > Layer provides absolutely no information about relative or absolute height > difference of objects which do not immediately cross or overlap. A change in > layer should not be used to indicate a change in elevation. A bridge is at > layer 1 even if it is only several feet above sea level while the peak of > Mount Everest is at layer 0 even though it is 8848 meters above sea level. > > Negative values do not imply that object is underground, use > location=underground for this purpose. > > Since it is a culvert, going under a road, I use layer=-1. If you tag it > layer=1, then you are saying the stream is above the road. > > > Err no. > I would prefer to tag the road at layer=1 as that is elevated compared to > what naturally existed before. Note this is a 'preference'. > I too take the path of less work compared to being absolutely technically > correct. > > Which might be correct in some instances, but looking at the picture, it > looks like it goes under the road. If you call the slab of concrete a > bridge, then layer=1 would be correct. > > Clifford > > > > I think the wiki is deceptive in claim level=0 does not imply anything. I > think it implies the"local ground level" ... examples; > on the peak of Everest this is 8848 meters above sea level. > A bridge on Lake Eyre (mean 15 metres below sea level) would be layer=1 .. > even with the bridge at 10 meters below sea level. (Note this 'lake' is a > salt lake and dry most of the time). > > The vast majority of waterways would be layer=0. > To say that surface water, while maintaining the same elevation is suddenly > layer=-1 when a roadway is placed over the top of it ... is technically > incorrect .. it is the road way that has been placed above "local ground > level".. > > Yes there are instances where surface water can change level .. those are > few. Not usual for culverts, as it is the road way is constructed on top of > what was there, the water way remains in the same place, at the same level > therefore the same layer. > > It is a very minor point. > > _______________________________________________ > Tagging mailing list > Tagging@openstreetmap.org > https://lists.openstreetmap.org/listinfo/tagging > _______________________________________________ Tagging mailing list Tagging@openstreetmap.org https://lists.openstreetmap.org/listinfo/tagging
