[Tagging] Comments wanted: Placement

Ronnie Soak chaoschaos0909 at googlemail.com
Fri Dec 21 11:08:19 GMT 2012

Hi Martin,

>> 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.

We don't force anybody to use a certain style. But we still say: If
you don't use the style we use, your work will neither be rendered nor
used by other consumers.
Well, let's say we just use use a very mild form of force, ok?
I think everybody who is willing to use your additional tag would also
be willing to follow a certain 'convention' when it comes to the
placement of the way.
The only task would be to design that convention in a way that works
well with all the roads that doesn't follow it.
'Line between directions' for single-way highways will probably only
be off by half a lane in most instances. The same for 'middle of
middle lane' (odd lanes) or 'line between middle lanes' (even lanes)
on two-way highways.
I see that without an extra tag, a consumer can't decide if the way
follows the convention or not. But that is the reason we kept the
possible error at a minimum.

> 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.

I remember a proposal (or at least a discussion) where the lanes=* key
had values for 'starting lane left' or 'ending lane right' etc. This,
together with the lanes count before and after and a consistent
convention on where the way is placed in reference to the lanes is
enough to give you a rendering of which lanes continue and which end.
(I think this was shot down because it needs so much splitting of the
ways. But so does placement=*.)

>> 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.

I would not put 'changing the beginning of a maxspeed zone by 4m' and
'completely destroying the lanes rendering' in the same category
But both will happen if I move a single node by a mere 4m without
looking at the tags.

>> (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 ;-)

So I whisper: there isn't so much effort if the tool support is good
and you stay above max zoom level.
But if you WANT to add that much detail, it is possible and will give
good gain. Also it will solve a lot of problems with one scheme
instead of several ones like your placement, the junction discussions,
the trunk/accelearation/decelaration lines discussion, the
legal/physical lane seperation discussion etc... But now I better shut


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