On 12/04/2011 09:38, Peter Miller wrote:
On 11 April 2011 23:39, SomeoneElse <li...@mail.atownsend.org.uk
<mailto:li...@mail.atownsend.org.uk>> wrote:
On 9 April 2011 08:15, Peter Miller
<peter.mil...@itoworld.com
<mailto:peter.mil...@itoworld.com>
<mailto:peter.mil...@itoworld.com
<mailto:peter.mil...@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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