[Tagging] Let's get (quite) rid of units and their multiples in OSM values

Paul Allen pla16021 at gmail.com
Fri Jul 27 19:20:28 UTC 2018

On Fri, Jul 27, 2018 at 6:48 PM, Kevin Kenny <kevin.b.kenny+osm at gmail.com>

> I'm all for SI units for things like voltages and elevations. I'm
> perfectly fine with tagging the elevation of Slide Mountain as 1274
> metres and letting a US data consumer convert that to 4180 feet.

I respectfully disagree.  One reason is of rounding errors in conversions,
as somebody said
earlier in the thread.  The other reason is one you imply below.

> Regulatory things like maxspeed=* should have the unit in the tag, and
> they should be in the same units that the signs are in. A sign reading
> 'Speed limit 25 mph' means 25 mph, and entering 40.2336 km/h loses the
> information that the regulatory signs are in US customary units.


Not +1 because this reasoning applies to *everything.*

If you're navigating somewhere unfamiliar to you and GPS isn't giving you an
accurate signal, what you're interested in is what signs actually *say.*
when you're in confusing territory a speed sign, or a bridge clearance, or
may be a significant clue.  Knowing that the speed limit is 40.2336 km/h
doesn't tell
you to look for a sign saying 25 mph.  You need both (so you don't break
the speed
limit), and I hope advances in rendering will eventually allow both (see
Wikimedia project
to provide multilingual mapping) to be displayable.

Actually, you only need both if you take your own car to a different
country, so your car
speedo is marked in km/h and the signs are mph.  Because if you rent a car
almost certain to get one where the speedo is marked in the appropriate
unit.  Actually,
it's been many decades since I've seen speedos that were not marked in both
and km/h, but it may be different in other countries.

That just leaves bridge clearances which will cause problems.  But even
driving in unfamiliar parts of their own country can get that wrong.  See
this youtube
channel for amusing videos about a bridge with 11' 8" clearance and people
don't understand their vehicle needs more clearance than that:

The alternative is to tag in SI units, accept rounding errors in some
countries, and
then tag US (and other country) speed limits with something like
Much cleaner to tag in whatever units are actually used and do conversions
on the
display side rather than the data entry side.

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