________________________________ >From: David Earl <da...@frankieandshadow.com> >To: osm <talk@openstreetmap.org> >Sent: Thursday, 22 January, 2009 13:51:16 >Subject: [OSM-talk] When is a bridge not a bridge? > >In view of some changes that I've seen going through in my area >recently, I'd be interested to know people's opinion on what constitutes >a bridge. In particular to what extent are the approaches part of the >bridge? I know I'm likely to hear wildly contradictory answers and >there's probably no right answer. > ______________________ > / \ > / \ > / \ >____/ \______ > >Are the ramps part of the bridge? If they are on solid embankments? If >they are a lattice structure supported on pillars, perhaps like >intermediate supports of the bridge itself? If they have parapets or >not? Or do people feel the bit marked as bridge should strictly be only >the span (or spans) itself? There is a set of ramps to a flyover: http://openstreetmap.org/?lat=-16.399543&lon=-71.542044&zoom=18&layers=B000FTT where I decided the ramps should be tagged as layer=1, bridge=yes. The reasoning was that it is possible to walk under these areas as it is a structure with pillars. OK the end point doesn't exactly coincide with where you can no longer walk underneath it, but that was at least my logic. As the layer tag signifies a vertical separation, I think it should be used where there is at least the possibility of multiple items at the same location. In other bridges, I have tried to make the bridge part stop where you can no longer pass underneath it. Often of course, this ends up being an estimate as I don't bother to take a waypoint while looking over the edge of the bridge to see where the gap stops! Donald
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