[Talk-GB] Speed limits

Dave Stubbs osm.list at randomjunk.co.uk
Thu Sep 20 11:04:10 BST 2007

On 20/09/2007, Richard Fairhurst <richard at systemed.net> wrote:
> Dave Stubbs wrote:
> > I came across a speed limit in Windsor Great Park a few weeks back for
> 38mph
> > which is a little odd... I'm not going to encode that as maxspeed=61.1as
> > that would seem silly.
> There are signs on a few canals in Leicestershire which say, in a nice
> little red circle, "6.43 km/h". I kid you not.
> The Environment Agency did it the sensible way. When they introduced a
> speed limit on the Thames, they purposefully chose 5mph because it'd
> be easy to sign as 8km/h if that was ever required.
> Anyway, back to the point, I'm not sure about the point of using
> "maxspeed_units" as a separate tag - it's adding an extra point of
> failure (what if the tag's removed? what if a client sees one tag and
> ignores the other?) and it's more of a faff to edit. Most importantly,
> it's another thing to remember - OSM tagging is difficult enough for
> the beginner without expanding the vocabulary needlessly.

Yeah, the vague point was that a something unable to parse mph, or xxx unit
used in xxx country could then try and fall back to the km version if it's
been entered explicitly.
Personally I'd rather just stick mph on (and have been actually, for all the
2 roads I've ever added a speed limit to).
I only suggested something else because the map features page explicitly
says it's km/h. Although this could be altered to say it's /default/ is km/h
if units are not supplied.

I think it's probably better to add the units to the tag value rather than
add an extra tag for units though, because then at least a stupid using
program will bug out when parsing instead of assuming the speed limit is way
too big/small because they didn't know about the units tag. Or at least
there's a greater chance of that. I think more users are likely to "get" it
that way too... too many tags confuse the mind.
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