On Thu, Jan 28, 2010 at 7:39 PM, Dale Puch <dale.p...@gmail.com> wrote:
Is it just a (very wide) road above? (layer 0) The road above would be Bridge=yes layer=1
Is it building or park above (with or without roads)? Tunnel=yes layer=-1 and the stuff above would be layer 0
I'm not sure which is in the picture, but the one with Chestnut Street is interesting. http://www.openstreetmap.org/edit?lat=39.947699&lon=-75.141691&zoom=18&layers=B000FTF
If you're going to put I-95 at layer=-1 (which I suppose you have to do due to the park), then I think Chestnut Street is a good candidate for layer=0 and bridge=yes. Then I guess you'd have to split Chestnut Street before it crosses Columbus and make it bridge=yes layer=1.
It appears to me that I-95 is below the level of the surrounding surface streets from about Market St down to Catharine St, and should be layer=-1. I suggest:
- Market Street overpass: bridge=yes, layer=1
- I-95 segment from Market St. overpass, south to ~ Catharine St : layer=-1
- Chestnut St, Walnut St, Dock St, Spruce St, South St overpasses: bridge=yes (no layer tag)
- Park(s): No layer tag
Spruce and Dock may not be necessarily be considered bridges. I'm not sure it matters much whether they are tagged as such.
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 think part of the confusion here is that some believe that bridge=yes implies elevation, which I don't believe. It just means that it crosses something less elevated. There may be a more precise civil engineering definition also - I try to tag roadway bridges and tunnels according to how the state or local engineers have categorized them. This generally results in more bridges than would otherwise be tagged, particularly those roads that cross sunken flood control channels, and areas with sunken freeways and many overpasses that are at street level.
Alan Mintz <alan_mintz+...@earthlink.net>
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