[Tagging] Comments wanted: Placement

Martin Vonwald imagic.osm at gmail.com
Fri Dec 21 10:40:03 GMT 2012

HI Ronnie!

2012/12/21 Ronnie Soak <chaoschaos0909 at googlemail.com>:
> I surely get the intention of enabeling renderers of any kind to draw
> more precice representations of lanes on a way.
> But I have two comments for you:
> 1. I think it PARTLY IS about position. Your tag does two things:
> allowing the renderers to position the lanes correctly in reference to
> the way and it allows the renderes to know which lanes continue and
> which start/end if the lanes count changes.
> You may be only interested in the second part, but the first part is
> still a valid use of it.

I'm definitively interested in both parts. My comment about position
was related to GPS devices which are not precise enough to tell you in
which lane you are (which might or might not be true - I'll not
comment on this). With this tagging we know the position of the lanes
within the outline of the road and we know the course of the lanes
more precisely (not perfectly).

If the GPS is precise enough to tell us on what lane we are is nice
but not really relevant here.

> 2. I have problems with the tag because it is (to my knowledge) the
> first 'meta-tag' to be actively used by consumers.
> It doesn't describe a feature of the real world but how a feature is
> described by our tagging.
> I much rather would like to see this information embedded in the
> existing tags like e.g. the lanes=* tag itself or by one of the
> various lane connection schemes.
> This would also fullfil the second use-case mentioned above.

How would you do that? The problem is: the OSM-way is drawn somewhere.
Some people draw in the middle of the road most of the time, others as
often as possible. Others draw the OSM-way between the two driving
directions which is not the middle of the road if we have a different
number of lanes in both directions. Some prefer to draw the OSM-way
straight even on junctions/exits (see second example in "Motorway
exit"). We will never be able - and we don't want to - force everyone
to use some specific mapping style. This tagging should gracefully
solve this problem: allow people to use their preferred mapping style
but also allow somehow to identify the style.

Neither the lanes-key nor any lane connection scheme can solve this.
Again - for example - look at the second image of "Motorway exit". It
is assumed that you know the lane count and the lane connectivity, but
without the information about the placement of the OSM-way in section
3 a consumer has no mean determining the course of the lanes.

> Imho introducing a tag that says how other tags work will make it more
> complicated for for data contributors, especially if this is
> introduces to other schemes where
> more than one possibility of tagging exists (public transportation,
> house numbers, etc.). It also has the chance of getting out of sync if
> some one changes the original tag (or in your case the relative
> position of the way)
> but doesn't change the meta-tag accordingly.

Absolutely correct - as with nearly all other tags. Someone moves a
node for any reason. But on that node a traffic sign is mapped. Or its
a connection between two ways and the maxspeed changes. Or the lane
count. Or anything else. Information is now out of sync. All the same.

> (Actually, I'm in favor of drawing the lanes seperately and even using
> areas, putting them into a relation to form the actual highway and
> letting the editors handle them just as one way in every but the
> closest zoom level.
> But I know that this is opposed to by the majority, so I'm mentioning
> this very very quietly.)

I didn't hear you ;-) My silent opinion: much to much effort for much
to less gain (except on complex junctions). You get nearly(!) the same
result with just a bunch of tags on one single way. But I didn't say
anything ;-)


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