[OSM-talk] Superways again

Nigel Magnay nigel.magnay at gmail.com
Sat Mar 17 15:58:30 GMT 2007


"Superways" (or paths, as I prefer) are hierarchical, so a single 'superway'
tag is not always sufficient and you need to make sure it's a correctly
ordered list.

I'm sure you *could* do it with tags, but because tags are freeform, you can
end up with a lot of unintentionally invalid data because they don't enforce
any structure. And I find it a frustratingly reductionist argument - why not
go the whole hog, abandon everything and make *everything* tags (which is,
after all, equivalent to a triplestore) - well, because it's inefficient,
and we ought to be modelling the fundamentals properly.

I'm pretty sure the output format could be transformed for 'renderers' to
pretend to be segment/ways, and you could probably even find a reasonable
way to round-trip to editors. But I'm also not convinced it's worth it -
it's not like we've got billions of editing packages out there - this topic
has been going on for about a year; even if there were agreement, it's not
going to suddenly change overnight. If it does change I'm sure there'll be
loads of time for the editors to catch up.



On 16/03/07, John McKerrell <john at mckerrell.net> wrote:
>
> I was putting together a response about how I thought perhaps it
> would be better to just name these "groups" rather than "superways"
> as I believe "superway" implies extra meaning that isn't intended.
> Basically all we're trying to do is assign tags to groups of ways
> without having to do it to each way, or have an easy method of
> selecting multiple ways.
>
> Then I realised that surely we have a method, tagging.
>
> Purely as a hypothetical example which I'm definitely not
> recommending, we could have superways by adding a superway tag to
> ways. It would contain a number.
>
> This assumes that we have facilities for selecting ways in editors,
> or downloading way information, filtered by specific tags.
>
> Once I realised that we already have the ability, I kinda realised
> that we don't actually need this superway tag, we just need to
> properly tag our information. For instance, want to select all of the
> ways that constitute the M1 motorway? Do a query (API or editor,
> whatever) for ref=M1 and highway=motorway. I realise that this would
> pull out a motorway in another country that had the ref M1, but I
> think that either that's valid, or the UK motorway should have
> further tags identifying it as being UK specific which you could
> further use. I don't know that an anonymous "group" would be a better
> solution.
>
> As an illustration, I'll go through your examples below showing how
> tagging could solve this, but just in case anyone stops reading here
> I'm not saying that this is is my final thought on how this should be
> handled, more "I've sat down, thought this through myself and these
> are my personal conclusions". Feel free to try to persuade me
> otherwise :-)
>
> So, illustrations:
>
> On 16 Mar 2007, at 16:31, David Earl wrote:
>
> > There are then lots of advantages to grouping such ways.
> >
> > * If you break a Way at a bridge, you can group the three Ways
> > (either side
> > and the bridge itself) so their commonality (it's the same road)
> > can be
> > represented (and so on along the road).
>
> highway=unclassified and name="Seddon Road" and postal_code=L19
>
> >
> > * An estate road with many branches can be represented as a whole.
>
> highway=residential and name="Rabbit Warren" and postal_code=E17
>
> >
> > * If you want to represent a bus route, the route tag in theory
> > allows this,
> > but in practice you can't put more than one route on the same Way,
> > so it
> > can't also be a different bus route or a cycle network route, and
> > the route
> > isn't coherent in any useful way - you have to search for where it
> > goes
> > next. So grouping ways to represent the concept of route would be
> > helpful.
> > Note this means ways can belong to more than one superway.
>
> Hmm... I'm certainly less sure about this. Bus routes and cycle
> routes should probably be separate tags, but multiple bus routes...
> I'd be tempted to say this is a problem with tags not allowing
> multiple values that we might look at solving.
>
> >
> > * A non-roundabout and non-node junction could be represented
> > (together with
> > its name or number) as a bag of ways (consider a grade separated
> > single
> > carriageway with four slip roads, or a cloverleaf).
>
> Give everything junction_ref=5 and ref=M6
>
> Actually, another reason that I've just thought that creating
> anonymous groups doesn't solve anything is that they're just that,
> anonymous, how do we then label them? We add tags to them, but what
> if someone creates a group with ref tag "M6", and then someone else
> creates another group with ref tag "M6" in another country, now
> they'll both come up.
>
> Also, I realise that this all assumes we have ways to filter by tags,
> but I think adding that capability to the API would be a lot easier
> than bringing in a new data type. Also searching by tags can easily
> be added to the editors (and of course is already there in josm,
> though it could probably do with being extended).
>
> Oh well, if David didn't like the blue touch paper I'm sure I just
> have, I'm popping out now so I'll be interested to see if my mailbox
> has blown up by the time I come back ;-)
>
> John
>
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