On Fri, Jul 16, 2010 at 4:55 PM, Anthony <o...@inbox.org> wrote: > On Fri, Jul 16, 2010 at 4:39 PM, David ``Smith'' <vidthe...@gmail.com> > wrote: >> >> Add to that >> grade_separated=* and you would indeed describe what is physically a >> freeway/motorway. > > What's the point of grade_separated=*? I thought that was covered by > bridge/tunnel=yes and the lack of sharing of nodes at the point where two > roads cross.
Technically you're right. But practically, grade_separated=* offers a /summary/ characteristic about the linear road. A nice map will display the difference between freeways (entirely grade-separated) and expressways (partially or not at all grade-separated) by choosing different line styles for each. The line style is applied along a linear path, whereas your suggested test (sharing of nodes or lack thereof) only provides results at discreet points along the road. That information can, theoretically, be then applied to the length of the road by a kind of "nearest-determination" method, or by a less-sophisticated per-way AND operation; but then on roads that have partial grade separation — many expressways — you'd have a weird dash-dot alternation between freeway and expressway classification. A useful map should only mark a road as a freeway where it consistently has grade separation from every crossroad. Not to mention, the test you suggested would have to be performed by every application that wants to know whether the road is (in summary) grade-separated or not; in the case of renderers, if this analysis is implemented at all, the mediocre result would almost certainly be generated as a kind of pseudo-tag anyway. We might as well just tag it from the start, using human judgement. -- David "Smith" a.k.a. Vid the Kid a.k.a. Bír'd'in Does this font make me look fat? _______________________________________________ Tagging mailing list Tagging@openstreetmap.org http://lists.openstreetmap.org/listinfo/tagging