[Tagging] Another reset on roundabouts

Martin Vonwald imagic.osm at gmail.com
Fri May 18 08:38:09 BST 2012


Good morning Toby,

You correctly identified a few of our problems.

At first let's have a look on a finding of Andrew Chadwick about the
usage of highway=mini_roundabouts a few days ago:
_______________________________________
For a random sampling of 100 nodes tagged highway=mini_roundabout from
Josh's set, I visually classified as

     1 "tc? island traffic calming of some sort"
     2 "parking"   (either an aisle
    10 "j" (ordinary junction: note that imagery could pre-date a
roundabout being built)
    15 "?" (can't tell: Bing imagery is too blurry or it's not clear)
    19 "tc"  (turning circle at the end of a road, with or without a
solid centre)
    23 "r"   (solid-centred roundabout you physically cannot drive over)
    30 "m"   (paint- or bump-centred mini roundabout, "traversable")
_______________________________________

What does this tell us? What do you think any data consumer should
treat a node tagged with highway=mini_roundabout?

If our data is completely inconsistent as in this case it is
worthless. I don't know about you, but I would like my work to be
actually used by someone. To achieve this we need some clean up, which
as every clean up raises some dust. And by "clean up" I mean not a
redefinition of any tag. We did not, should not - and as you pointed
out - could not (successfully) change the definition of any tag that
is widely used.

In the case of junction=roundabout I started to collect information
from different wiki articles and previous discussions, asked for some
photos, made a draft of a reworked article and started a discussion in
three mailings lists. The discussion was fruitful, showed some
difficulties and revealed some sources of the bad data. We agreed on
some minor changes in the tagging scheme (junction=roundabout also on
a node and highway=turning_loop) for easier tagging. After we reached
some level of agreement I updated the wiki yesterday evening (and we
all know what happened then, but we forget about this now). So this is
more or less how a good clean up should look like, at least in my
opinion.
Is there anything that could be improved in your opinion?

What is left now is that editors and renderers must be updated to the
changes in the tagging scheme. And as you pointed out correctly, we
need some better wording in the presets of editors to prevent
incorrect usage. Hopefully this can be achieved within the near
future.

Do you have any suggestion how to change the presets for
mini-roundabouts? The term "mini-roundabout" is very misleading so we
need some very good, crystal clear and short description for it. Any
idea is very welcomed!

regards,
Martin

2012/5/18 Toby Murray <toby.murray at gmail.com>:
> On Thu, May 17, 2012 at 8:59 PM, Andrew Errington <erringtona at gmail.com> wrote:
>> On Fri, May 18, 2012 at 7:21 AM, Toby Murray <toby.murray at gmail.com> wrote:
>>> Otherwise we can pontificate all we want on the mailing list but
>>> people who are not familiar with the concept of a "real"
>>> mini-roundabout WILL still use this tag for "small roundabouts" with
>>> non-traversable centers. That's just reality. Maybe change the display
>>> label to "traversable roundabout" or something?
>>
>> If the definition is clear in the wiki then there should be no
>> problem.  Anyone discovering something in the database that does not
>> match the definition is free to correct it.
>
> By all means, make the wiki crystal clear. But how many of the mappers
> who have added mini roundabouts outside of the UK do you think checked
> the wiki before they tagged a node? 1%? No. They saw the preset in
> their editor (both JOSM and P2 have one) and clicked on it. That's
> what I did. I had no idea there was such a thing as a "mini
> roundabout" that met strict requirements until months after tagging
> several intersections in my city as such. And I am not a casual
> mapper.
>
>> In real life the definition is quite clear.
>
> Only to people who actually know what a mini roundabout is.
>
>> We have two distinct nouns, 'roundabout' and 'mini-roundabout'.
>> Although 'mini-roundabout' is made from two words which have a
>> well-understood meaning, the compound word has its own specific
>> meaning.  Adding a further definition (such as 'traversable
>> roundabout') is not necessary, since, by definition, a mini-roundabout
>> is traversable, and a roundabout is not.
>
> Ask anyone who has never seen a true mini roundabout. I guarantee
> their response will be "oh it's a small roundabout." I'm not saying
> you are wrong. I'm saying without further clarification the definition
> of a mini roundabout in OSM will be worthless because people WILL use
> it for things that are not true mini roundabouts. So either we accept
> that the definition will change based on region or we have to present
> it to the user differently.
>
>> 'Roundabout' on a node means this is a
>> small roundabout, but it was too much effort (or too tedious) to draw
>> a circular way.  It is not traversable, and traffic must 'go around'
>> it based on the local rules for direction and giving way.  Anyone who
>> discovers 'roundabout' on a node is free to re-draw it as a small
>> circular way.  The net effect to routing should be negligible.
>
> I agree with this. It's just that the JOSM validator complains to high
> heaven if you put junction=roundabout on a node and P2 doesn't offer
> it as an option when you have a node selected. Oh but what's this I
> see in the presets? A mini roundabout? Oh, that's perfect! I'll use
> that instead.
>
>> I think the problem is that we use 'mini-roundabout' with highway=*
>> and 'roundabout' with junction=*.  In my opinion they should both be
>> junction=*, with 'mini-roundabout' restricted to nodes, and
>> 'roundabout' applicable to nodes or circular ways.  Furthermore, when
>> applied to a node we should probably encourage the tag direction=*
>> although some software can probably figure that out.
>
> I have no problem with this either although if history is any
> indicator, changing tags that are actually in use is nearly impossible
> so good luck with that.
>
> Again, I'm not saying you are wrong on how things SHOULD be. I'm just
> pointing out that your view is skewed by the fact that you know such a
> thing as a mini roundabout exists in real life.
>
> Toby
>
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