I've been trying to figure out how to tag some moderately complex exit ramp systems when a single motorway_junction doesn't seem adequate. An email to the newbies list led to an IRC discussion that led to a solution that I like, so I wanted to present it here to see what other people think and possibly what other people have done in similar situations.
As background, most highway exits are simple and a motorway_junction with a ref= for the exit number captures all the important information about the exit. That approach works best, though, if there's only one destination from the exit. I know several places where the reality is slightly more complicated than that. One example is the exit from westbound I-70 in Maryland (in the US) onto I-695[0]; there is one ramp from I-70 with exit number 91 that splits a short while later into exits 91A (I-695 southbound) and 91B (I-695 northbound). I want to be able to capture all of that information in OpenStreetMap so that a theoretical routing agent can say, e.g., "Take exit 91 to the right, then take exit 91A to the left." [0]: I-70 westbound exit 91 http://osm.org/go/ZZd8vPYT The IRC discussion pointed out that this falls more or less into the same domain as the destination_sign relation. The only thing it's missing is the exit number. What I think would work would be to use the destination_sign relation with the destination= tag containing the target road (I-695, in my example), possibly extended with other destinations from the signs in order of increasing distance (so exit 91A might have "destination=I-695; Glen Burnie; Washington"); and the ref= tag containing the exit number (so exit 91A would have "ref=91A"). I'd like to know what other people think about this idea. What other approaches have people used for my situation? One person on IRC suggested that ref= on the destination_sign relation sould be the ref of the destination road, but I think it makes more sense to have it as the exit number (perhaps there could be a destination_ref= tag). Are there any opinions one way or the other on that? -- ...computer contrarian of the first order... / http://aperiodic.net/phil/ PGP: 026A27F2 print: D200 5BDB FC4B B24A 9248 9F7A 4322 2D22 026A 27F2 --- -- Steal this tagline. I did. ---- --- -- _______________________________________________ talk mailing list [email protected] http://lists.openstreetmap.org/listinfo/talk
