On 14 April 2011 12:27, Chris Hill <o...@raggedred.net> wrote: > On 14/04/11 11:42, Richard Fairhurst wrote: > >> Peter Miller wrote: >> > So the proposal is now: >> >>> >>> maxspeed:type=GB:national_single|GB:national_dual|GB:motorway|GB:restricted >>> >> I may be missing the point on all of this, but: >> >> Why are we doing this? >> >> In OSM we optimise for the mapper, not the data consumer. That means we >> tag >> exceptions, not majorities. >> >> So if you have highway=motorway, the consumer can assume the national >> speed >> limit applies, which is 70mph; no need for a maxspeed or maxspeed:type >> tag. >> If you have highway=trunk (or anything down to unclassified), assume the >> national speed limit applies, which is currently 60mph if it's a single >> carriageway, 70mph if it's a dual[1]. And so on. >> >> Where this isn't true, you put a maxspeed tag on. This works for pretty >> much >> everything from 30mph on B roads through villages to 50mph on rural A >> roads >> to 70mph on the A55 Special Road. No need for a maxspeed:type tag at all. >> >> Have I missed something blindingly obvious? >> >> cheers >> Richard >> >> [1] Perhaps the only difficulty is that there's currently no trivial way >> to >> identify what's a dual carriageway and what isn't, short of doing clever >> geometry stuff. But that's easy to fix: either a relation (spit) or >> preferably something simple like dual_carriageway=yes. >> > +1 >
There would be a number of benefits of wrapping dual carriageways up into a relation saying 'these two ways are part of a single dual-carriageway'. One is to get round the maxspeed problem, but it also provides information needed to create overview mapping with a single way for a dual carriageway. Here is one I created some time back (a long time back actually, it is relation 2493!).[1] I was also interested in wrapping all of the ways that make up a junction into a 'interchange' relation. Again, here is one I made earlier.[2] In response to Richard - thanks, that is a good example. Here is the equivalent page for maxspeed which has lots of information in it but is way off being useful to a parser! [3] [1] http://www.openstreetmap.org/browse/relation/2493 [2] http://www.openstreetmap.org/browse/relation/2473 [3] http://wiki.openstreetmap.org/wiki/OSM_tags_for_routing/Maxspeed Peter > -- > Cheers, Chris > user: chillly > > > > _______________________________________________ > Talk-GB mailing list > Talk-GB@openstreetmap.org > http://lists.openstreetmap.org/listinfo/talk-gb >
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