While sympathetic to the underlying need being discussed in this thread, I suspect there is a further problem. Although a way has an intrinsic sense in OSM, this is fairly volatile! All it needs is someone to reverse a way - and this can happen rather easily, say, when combining two ways with the same tags but different senses (yes - there is a warning but it's all too easy to click through). Reversing the ways then, of course, reverses the 'left' and 'right' descriptors with their differing tags! This leads me to wonder whether an absolute sense (north, south, etc.) is still better even though it might require that a way is divided a bit. Most ways do have a 'general' compass direction for long segments even if this is often more human-obvious than machine-obvious. The main exceptions are likely to be short residential streets on housing developments etc. - 'circles' etc. - but these are less likely to require unilateral tagging.
Btw, I have encountered the same problem with canals. Some mappers describe towpaths as being 'left' or 'right'. Personally, I prefer to map the towpath as a separate way alongside the canal - with the added advantage that this allows me to tag the towpath, e.g. with access rights, surface condition, barriers, reference numbers, route relations, etc. Perhaps this would also be a better approach for e.g. cycleways alongside motor roads? Although, I have to admit that it doesnt solve the problem of unilateral naming. Mike Harris -----Original Message----- From: David Earl [mailto:[email protected]] Sent: 17 February 2009 11:10 To: Andy Allan Cc: Norbert Hoffmann; [email protected] Subject: Re: [OSM-talk] [tagging] RFC :left/:right (asymmetrical roadside features) On 17/02/2009 10:36, Andy Allan wrote: > On Mon, Feb 16, 2009 at 7:11 PM, Norbert Hoffmann > <[email protected]> wrote: >> Andy Allan wrote: >> >>> And every time using :left and :right comes up, we all have a big >>> discussion about it and then nobody pays any attention and it comes >>> up again a few months later. >> Perhaps this is because the concept "left"<>"right" is so simple - >> and the aversion against editors, that are not totally key-ignorant >> is not so easy to understand. > > And nobody pays attention. The main problem is that two-way roads have > no inherent, real-world, "direction" - neither side of the road is the > right or the left. Or rather, both sides of the road are the right or > the left, depending on which way you are facing. The only place that > right and left has any intrinsic sense is on one-way roads, which *do* > have an inherent direction (and signs to that effect). > > Let's say you have a church beside a road. If it's a oneway street, it > makes some kind of sense to say "it's halfway along the road, over on > the left". > > Let's say you have a church beside a two-way road. If I said "it's > halfway along the road, over on the right", you still wouldn't know > which side of the road it is on. > > Now the problem is that most people at the moment in OpenStreetMap are > tech-heads, and are so used to mental constructs and abstractions like > every road having a completely arbitrary intrinsic direction - but > that doesn't mean it's a great idea. Editor support is less important > - and far easier to fix - than explaining to all the people who don't > even realise that all roads have a direction in openstreetmap - and > except for oneway roads, I have no idea which ways are pointing in > which directions, and it shouldn't be important unless it *has* to be > important. Real People often talk about "the church on the left when you're heading towards somewhereville", so it's not *that* alien a concept. And in terms of the other concepts you have to understand to edit the map, it's hardly a big one. And you do already have to know about it - for one way streets and also for rivers and also for boundaries where exactly this left/right issue arises. So I think you're overstating the problem with this, and the reason it isn't widely adopted is because there has been no consensus in the past, not because it is fundamentally hard. There's only really two ways to deal with this geometrical relationship: relative or absolute. left/right is relative and suffers from lack of a "natural" direction to base it on; north/south/east/west is absolute, so is independent of any reversals done in the editor, but suffers badly on roads which turn more than 90 - 180 degrees - so you'd have to split them, which is just as arbitrary a rule as using the direction, though probably rarer. Since for any N people discussing something in OSM there always seem to be N+1 opinions, the only way this is likely to be resolved is if people just do it (in their preferred way) and see if one of them wins. It's more likely to win if the renderers act on it. Incidentally, :left/:right (or :north, etc) have a problem with languages on names. So if the name on the left (north) is different, using name:left (name:north) would have to be dealt with as a special case as name:x is usually used with x as a language. David _______________________________________________ talk mailing list [email protected] http://lists.openstreetmap.org/listinfo/talk
