On Fri, Jul 27, 2018 at 6:48 PM, Kevin Kenny <kevin.b.kenny+...@gmail.com> wrote:
> 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. > +0.5 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.* Because when you're in confusing territory a speed sign, or a bridge clearance, or whatever 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 you're 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 mph and km/h, but it may be different in other countries. That just leaves bridge clearances which will cause problems. But even people 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 who don't understand their vehicle needs more clearance than that: https://www.youtube.com/channel/UCXX0RWOIBjt4o3ziHu-6a5A 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 customary_unit=mph. Much cleaner to tag in whatever units are actually used and do conversions on the display side rather than the data entry side. -- Paul
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