[Talk-GB] Maxspeed tagging for the UK

Peter Miller peter.miller at itoworld.com
Tue Apr 12 11:49:44 BST 2011

I apologise for editing too soon and having taken silence as agreement. I
will not any more editing of maxspeed while we resolve this issue.

In my defense I would note again that a considerable percentage of
unrestricted roads in the UK had already been tagged in numeric format and
that my manual edits were about improving consistency rather than going
against the majority or even a large minority.

Personally I don't care as much about which standard we adopt as to the idea
that we have a preferred format that is documented and is compatible with
other countries schemes and which is readily available for routers to use
and is implemented! Mot people will hold off mapping speed limits until this
is resolved.

If we use the 'national' approach then in my opinion routers must have
simple unambiguous access the relevant numeric speed which can either be
included in the maxspeed field or in some suitable supporting field. If we
use a supporting field then we need some useful defaults. In either case we
need to agree which we prefer and what the text is for single carriageway,
dual carriageway and motorway.



On 12 April 2011 11:22, Jerry Clough : SK53 on OSM <SK53_osm at yahoo.co.uk>wrote:

>  On 12/04/2011 09:38, Peter Miller wrote:
> On 11 April 2011 23:39, SomeoneElse <lists at mail.atownsend.org.uk> wrote:
>>>> On 9 April 2011 08:15, Peter Miller <peter.miller at itoworld.com <mailto:
>>>> peter.miller at itoworld.com>> wrote:
>>>>  ...
>>>>    We seem to be nudging towards something close to a conclusion.
>>>>    Can I suggest that the following two methods are valid, however
>>>>    the second one should be considered to be 'better' and where it is
>>>>    used then it should be retained to avoid edit warring.
>>>>  ...
>>        Method 2
>>>> maxspeed=60 mph
>>>>  maxspeed:type=GB:rural
>>>> source:maxspeed=survey
>> Great - someone has now changed a bunch of "maxspeed=national" locally to
>> me to to "maxspeed=60 mph".  Next I guess someone will come along and add
>> "source:maxspeed=i_was_sat_in_my_armchair_and_it_seemed_like_a_good_idea" or
>> similar?
>> We've lost the information that the sign is actually NOT a 60 mph sign.
>> Something like method 2 above would have avoided losing information
>> (although "GB:rural" is meaningless; if pushed, "GB:national" or some
>> variant would be better).
> The general conclusion of the discussion above was that where
> maxspeed=60mph is applied to a single carriageway road there is also a
> default 'maxspeed:type=GB:unrestricted' (or whatever value is decided on).
> This default (and the one for 70mph for motorways and dual-carriageways) was
> including to avoid burdening the mapper with another tag to add in most
> situations. The only 60 mph signs that need another tag are those rare cases
> where a single carriageway road does have a numeric speed limit.
> Fyi, about 95% of currently mapped speed limits in GB at speeds of 60mph
> and 70mph speed limits were already tagged as 'maxspeed=60' and
> 'maxspeed=70' when I first looked at this about 4 weeks ago leaving only
> about 5% tagged as national or nsl.
> I have been converting this remaining 5% over the past 2 weeks (with a
> brief delay while we discussed the principle on talk-gb after a reversion of
> one of my edits). I have had no complaints from others to my changes and
> only one reversion of one section of the A1 as I mentioned in my post. I
> take this as broad support for the changes.
> By tomorrow there will be next to no remaining 'national' and 'nls' speed
> limits in Britain other than in your patch around Macclesfied which I won't
> touch any more.
> There are also a small number (another 5%) of roads that are not in a
> recognised mph format, either because the mph is missing or because it is in
> km/h or for some other reason. I will be doing a copy-edit pass on these
> either fixing them if it is obvious or marking them with a fixme:maxspeed
> tag if not. I should be finished with that in about a week.
> Regards,
> Peter
>> Cheers,
>> Andy
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>  I think there has been a discussion: I'm a bit surprised that there was
> also an agreed consensus, let along one which justifies mass edits. And if
> pushed I would have said that the consensus was maxspeed=national.
> The discussion never pursued a number of outstanding issues. The most
> important of these being whether it would be useful to identify dual
> carriageways in general, rather than specifically for identifying speed
> limits (I believe that it would, the post-processing effort is high and
> there are sufficient anamolies to make it difficult to identify all
> satisfactorily). Others relate to relevant speed limits for different
> classes of vehicles, and finding suitable names for the additional tags.
> I was unhappy with the original mass edits which added unnecessary fixme
> tags and other curious tags to roads. To compound this with assuming that
> further mass edits would be acceptable seems way over the top.
> Suitable renders make a big difference by showing what is missing and
> encouraging people to be more proactive in mapping them. Andy Allan's new
> experiemental transport layer is a big bonus in that regard. Using such a
> render to drive tagging is less desirable, simply because it results in
> 'tagging for the renderer' type behaviour such as the creation of ways to
> supress display in the ITO OSM Analysis layer.
> I've not pitched my oar in until now. I had been quite happily using a
> numeric value for maxspeed, but the discussion on this list showed me the
> error of my ways. The main reason I'd used a value was a misguided belief
> that it would improve the times calculated by routers. I've been playing
> around with various OSM based routers, and they dont seem to make
> sophisticated use of this information. My impression is that most place
> speeds into buckets, and that they make assumptions along the lines of JOSM
> that a trunk is equivalent to a dual carriageway motorroad.
> My summary of what seemed sensible would be:
>     maxspeed=national or maxspeed=gb:national  /* with former preferred */
>    dual_carriageway=yes (or something similar)   /* preferred over variants
> which just refer to speed */
>    national=70 mph (or variants on this)                  /* xxx:type=*
> tags are horribly ambigous */
>    source:maxspeed=survey                                   /* don't change
> the meaning of the source namespace */
> It is important to keep the basic tagging required as simple as possible,
> maxspeed=national can be added as a preset to things like Potlatch with the
> appropriate sign. The need to add several additional tags, adjectival
> tagging, namespacing should be just that: optional not essential in tagging.
> Outside of people who write programs, who knows what a namespace is?
> Like it or not OSM tagging will always result in inconsistent values for
> attributes. Inisisting on a data type for tags has in the past resulted in
> horrors like maxspeed=80.467.
> Lastly, never assume that absence of messages is approval or acquiescence.
> It is always best to follow up, with "in a few days time I plan to perform
> edits x, y, z: please let me know if you have objections". Then do edits in
> a limited area, to see if you get further objections (in this case you have
> Andy & Steve raising issues).
> I recently became aware that the Data Working Group have a draft policy in
> this area:
> http://wiki.openstreetmap.org/wiki/Data_working_group/Mechanical_Edit_Policy.
> Jerry
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