On 14 April 2011 11:42, Richard Fairhurst <[email protected]> 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? > You note below the difficulty of establishing exactly what is a one way road and what is part of a dual carriageway. That is one complication that is worth remembering. There is also the difficulty of identifying which country you are in and therefore what lookup value you should use. Does the Ilse of Man have the same rules as England? Northern Ireland? Jersey? I have no idea and nor would someone from Japan. There is current the problem that no one has actually created a look-up table for the values that can be used by downstream systems and that is very hard to do when the rules for each country are different and when there is not even agreement on the tags within a country. You point about tagging for the mapper. I think it is shortsighted to tag in such a way that the downstream applications have a problem and indeed either ignore the data at all or get it wrong. If we did that universally then the UK would be the only ones using highway=motorway and Mapnik would need loads of rules to deal with highway=interstate, highway=autobaun, highway=autoroute etc etc. To respond the monxton either of the proposed systems will accommodate changes to rules as occurred in 1970s. Without a clear distinction about the jurisdiction and the exact distinction between a single and dual carriageway it can not. Regards, Peter > > 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. > > > > -- > View this message in context: > http://gis.638310.n2.nabble.com/Maxspeed-tagging-for-the-UK-tp6245995p6272282.html > Sent from the Great Britain mailing list archive at Nabble.com. > > _______________________________________________ > Talk-GB mailing list > [email protected] > http://lists.openstreetmap.org/listinfo/talk-gb >
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