[Tagging] Dispute prevention: meaning of lanes tag
a.errington at lancaster.ac.uk
Fri Apr 27 12:52:35 BST 2012
On Fri, 27 Apr 2012 18:54:26 Ilpo Järvinen wrote:
> On Fri, 27 Apr 2012, Andrew Errington wrote:
> > A lane count of 1.5 is very confusing. What does it mean? What is the
> > width of each lane? Is it really 1.5? Should it be 1.55, or 1.4, or
> > 1.6?
> ...No, it's not multiple of some magical "default lane width" like you
> imply. But simply _something_ between "normal" lanes=1 and "normal"
But the width=* tag tells you this. Specifically, the width tag tells you if
there will be a problem *for you*. Since I have never met you and I don't
know what vehicle you are using it would be presumptious of me to tell you
that there are 1.5 lanes. Also, it doesn't make sense to allow lanes=1.5 but
deny 1.55, 1.4, 1.68 or any other fractional value. What you are doing is
introducing a 'special' value with a special meaning. I think we should try
to avoid having to interpret special cases.
> > It's more useful to tell me width of the road. Then, if there is one
> > lane I can see maybe it's very wide, or if two lanes I can see maybe
> > they are very narrow.
> ...But how can I tag you this: A road which is lanes=1+wide _AND_
> lanes=2+narrow at the same time? ...You ask me to provide width and select
> one of those two, and that is what I oppose, unless you give me some real
> tag that is not width to tell that 'hey, there really isn't lanes marked
> (which makes it kind of lanes=1) but two can somewhat fit (which makes
> it kind of lanes=2 but not really because it's only "somewhat")'!
> ...What I would not want to do is to tag those lanes=1 because that's
> certainly a lie as anyone can clearly see after observing some
> bidirectional traffic there.
It's not a lie. A single lane may be bidirectional. In fact, in this case
you *should* tag it lanes=1. If oneway=yes is not present then it means one
> > In summary, I think simpler is better. A non-integer lane count is
> > useless. Use the width tag.
> I oppose using width tag (at least alone) for this because it won't
> convey the double meaning. Some other tag than width and tagging with
> lanes=2 perhaps (like I already suggested much earlier)?
I don't think there is a double meaning.
lanes=1 tells me there is one lane. It does not mean one direction, nor
should anyone assume that. I *think* you are saying that lanes=1.5 tells
me "this road is not really wide enough for two-way traffic, but there *is*
two-way traffic so if there is a car coming the other way you have to
For the purpose of discussion, let us assume that a road of 2.5 m width is too
narrow for cars to pass.
lanes=1 width=2.5 tells me the same thing (one narrow lane, cars travel both
directions, but only one direction at a time).
lanes=2 width=2.5 tells me the same thing (two very narrow lanes, cars travel
both directions, but only one direction at a time).
lanes=1 tells me the same thing (one lane implies cars cannot travel both
directions at the same time, but no oneway=yes tag implies cars can travel in
both directions. We don't know the width but there must have been a reason
for a mapper to tag it with lanes=1).
width=2.5 tells me the same thing (no lanes=* tag and no oneway=yes tag
implies two lanes, but both must be very narrow therefore cars can only
travel one direction at a time).
I don't think any of these assumptions are unreasonable, and they don't alter
the existing meaning of the tags, which I believe are already quite clear, so
we should use them and not alter them with special cases.
 I have made this sentence to interpret what lanes=1.5 means. If my
understanding is incorrect please state what lanes=1.5 actually means.
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