Hi, On Mon, Jan 28, 2008 at 07:16:25PM -0000, Andy Robinson (blackadder) wrote: > >> Why is it not a property like bridge, cutting etc. and > >> will it render correctly? Should it be changed to > >> viaduct=yes? > > > >Ewww, yuck... boolean flags. > > > >Personally I would tag as: > > > > railway=rail > > bridge=viaduct > > > > bridge and viaduct are two separate types of structure so > strictly speaking bridge=viaduct is incorrect.
They might be different to you as a civil engineer... to me a viaduct looks like lots of bridges next to each other (i.e. huh, what's the difference, really?) ;-) Actually, it's more of a thing I have about using on/off, yes/no, true/false type tags - they generally are not right in my opinion. For instance, take the same principle applied to roads highway=yes motorway=yes We use highway=motorway here - if nothing else it stops you doing the silly highway=yes motorway=yes secondary=yes Similarly, something can't be both a bridge and a viaduct. Therefore you want something like over=bridge or over=viaduct a) you reduce the keyspace, and b) you can't have bridge=yes viaduct=yes As usual in my case "over" is a bad name for a key. I guess that's why I stuck to the more generic "bridge" before, with "bridge=yes" being the general case. It's the same as saying bridge=suspension, rather than bridge=yes, suspension=yes (or even bridge_type=suspension - eugh). Maybe something like "transit=" would be better (in the sense of "how this way gets from A to B") and could then include tunnel, cutting, embankment, etc in the list of values as well as bridge and viaduct. Basically, I would say that every "object-type" key (i.e. not things like name=) should have as many non-coexistant values* as possible (if that makes sense), and that single flags (i.e. where a key only ever has one value) should be discouraged wherever possible. * i.e. you can't have both on the same "object", such as suspension and viaduct > We already use layer=+/-5 for setting display layering and > I always envisaged the same simple system could be used > for cuttings and embankments. Yes. I guess the issue here is that cuttings/embankments are usually drawn in on maps. Maybe it's a renderer problem. > I'd prefer to see railway=rail for all rail corridors and > a secondary tag for the type of service/stock used - ie > metrorail/subway/underground/freight etc etc etc Ditto to the above. railway=rail is basically the same as railway=yes if you say that. A railway can't be both subway and normal rail, so you therefore use railway=rail or railway=subway etc. If nothing else you know that it's some type or other of railway, without even having to look at the value (same for bridge, etc). Anyway, that's my computer science thinking - back to your civil engineer ideas... ;-) Cheers, -- Matthew _______________________________________________ talk mailing list talk@openstreetmap.org http://lists.openstreetmap.org/cgi-bin/mailman/listinfo/talk
