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On 06/04/11 15:55, Peter Miller wrote:
<blockquote
cite="mid:BANLkTi=td51_KrNXn58RB_4r3hHxUW9Zqg@mail.gmail.com"
type="cite"><br>
<br>
<div class="gmail_quote">On 6 April 2011 15:02, Chris Hill <span
dir="ltr"><<a moz-do-not-send="true"
href="mailto:osm@raggedred.net">osm@raggedred.net</a>></span>
wrote:<br>
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<div class="h5">On 06/04/11 14:22, Peter Miller wrote:<br>
<blockquote class="gmail_quote" style="margin: 0pt 0pt 0pt
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<br>
Do we have a preference for tagging unrestricted limits
in the UK? I say that because a section of the A1 is
beginning to look a bit war damaged (as in edit war).<br>
<br>
It started with maxspeed=national. I changed it to
maxspeed=70 mph. Christcf then added a 'source:maxspeed
= UK:nsl_dual' and also 'FIXME:nsl = inferred
dual-carriageway NSL - remove this tag once verified; if
this is a Special Road, remove the source:maxspeed tag
and add motorroad=yes'. And now c2r has changed maxspeed
back to national!<br>
<br>
Here is the way in question:<br>
<a moz-do-not-send="true"
href="http://www.openstreetmap.org/browse/way/3994397/history"
target="_blank">http://www.openstreetmap.org/browse/way/3994397/history</a><br>
<br>
My preference is to put a numeric speed in the maxspeed
field and something like 'UK:nsl_dual' in
source:maxspeed field, however I am not that keen on a
prolonged edit war on this and want to gauge wider
opinion.<br>
<br>
If it is ok to put something like 'national' in the
maxspeed field then what text options are appropriate
for the UK? 'national' seems too vague. 'UK:national' or
'GB:national' would fit with the recommended structure
as would 'UK:motorway', 'UK:nsl_dual' and
'UK:nsl_single' however I can find no guidance on that.<br>
<br>
Assuming we are supporting these second format then
where should the look-up table be that gives the values?
This page is having a go at it but doesn't seem to be
doing a very good job!<br>
<a moz-do-not-send="true"
href="http://wiki.openstreetmap.org/wiki/OSM_tags_for_routing/Maxspeed"
target="_blank">http://wiki.openstreetmap.org/wiki/OSM_tags_for_routing/Maxspeed</a><br>
<br>
Incidentally, I have also updated the key:maxspeed wiki
page so that it more clearly represents the tagging
recommendations and options available, in particular it
presents the two options for encoding implicit speed
limits well. Can people see if they agree with current
representation of opinion.<br>
<a moz-do-not-send="true"
href="http://wiki.openstreetmap.org/wiki/Key:maxspeed"
target="_blank">http://wiki.openstreetmap.org/wiki/Key:maxspeed</a><br>
<br>
Any thoughts?<br>
<br>
<br>
</blockquote>
</div>
</div>
I think we should tag what we see on the ground. The sign is
national speed limit, not 60 or 70 mph. The black & white
sign does not mean 60 mph or 70 mph for every vehicle, lorries
have lower limits for example. I currently don't tag maxspeed
on national speed limits, but this absence encourages the
nonsense that chriscf came up with, so if pushed I'd use
maxspeed:national . All of the roads being discussed are in
the UK, so they do not need UK: or GB: namespaces. This is a
geo-database after all.<br>
</blockquote>
<div><br>
I have a number of concerns:<br>
<br>
1) We have no agreement on maxspeed tagging in the UK which
means there is potential for edit warring as we have seen on
the A1 which will discourage further work.<br>
</div>
</div>
</blockquote>
I agree. That does not mean we need a complex scheme.<br>
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<div class="gmail_quote">
<div>
<br>
2) Our use of 'national' doesn't fit within schemes being used
in other countries which suggest a two letter country code
first. UK:national would be a recognition that this is an
issue and would avoid the need to accurate borders for all
countries which is I assume why the two letter code has been
adopted in the first place.<br>
</div>
</div>
</blockquote>
Not convinced. If I was creating a database of bird sightings I
wouldn't put bird:name in front of every sighting. Why does a geo
database need a location namespace?<br>
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cite="mid:BANLkTi=td51_KrNXn58RB_4r3hHxUW9Zqg@mail.gmail.com"
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<div>
<br>
3) There is no established mechanism that I can see to turn
the 'national' text into a numeric speed even if one does know
that it applies to the UK (similarly for a value of
BE:motorway incidentally). <br>
</div>
</div>
</blockquote>
Well establish one then. Why does this mean some complex scheme is
needed?<br>
<blockquote
cite="mid:BANLkTi=td51_KrNXn58RB_4r3hHxUW9Zqg@mail.gmail.com"
type="cite">
<div class="gmail_quote">
<div><br>
4) If the same text (for example 'national') is used for
motorways, dual carriageways and single carriageways then it
seems to be very difficult to establish if one is talking
about a one-way street that happens to also be a primary or
trunk road (and should therefore be 60 mph) or if it forms
half of a dual carriageway (and should therefore be 70 mph).
The only reliable method is to look for a parallel way next to
the way in question with same ref, the same class and the
opposite direction. Decisions relating to slip roads is also
troublesome and will vary by country.<br>
</div>
</div>
</blockquote>
Distinguishing between dual and single carriageways that are not
motorways might be an issue, but worth much complexity.<br>
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<div class="gmail_quote">
<div>
<br>
5) With reference to the fact that not all vehicles are
allowed to travel at the maximum speed then that also applies
to 50mph and numeric 60 mph limits where some vehicles (such
as mopeds) cannot legally travel at those speeds. How do you
suggest that these should be tagged?<br>
</div>
</div>
</blockquote>
I don't. Just tag maxspeed=national where a national speed limit
exists. Map users need to obey the speed limits on the road. Routers
can ask for the vehicle type and act accordingly. Why else would I
need to tag all the varieties?<br>
<blockquote
cite="mid:BANLkTi=td51_KrNXn58RB_4r3hHxUW9Zqg@mail.gmail.com"
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<div class="gmail_quote">
<div>
<br>
All in all, speed limits tagging still seems pretty flakey
which is a shame!<br>
<br>
</div>
</div>
</blockquote>
Mappers are scarce and precious. Every complex tagging scheme risks
scaring some away. Every complex tagging scheme risks mistakes and
horrendous bot updates. Think of mappers *first* in what ever you
dream up - they use that scheme over and over again. Put the burden
on programmers who only write the code to deal with each situation
once.<br>
<br>
If you can't explain the scheme to a newbie in ten seconds then it's
too complex. <br>
-- <br>
<pre class="moz-signature" cols="72">Cheers, Chris
user: chillly
</pre>
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