[OSM-talk] Map Features, maxspeed and maplint

[Shaun McDonald]

All units in osm should be the metric value, unless the units have  
been name spaced. Whenever I enter mph units, I use the tag  
maxspeed:mph=30 etc as this is the most accurate way of representing  
the data. I'm not going to spend time converting between mph and kph,  
when entering the data, that is for whoever uses the data to do. In my  
opinion, it is far better to use the local units, but always have it  
clear as to the units, when they are not metric/most  common.

Shaun

On 5 Oct 2008, at 13:45, Ed Loach wrote:

> I've not done much maxspeed tagging to date, for various reasons,  
> but the main one is that Map Features says that maxspeed should be  
> in km/h. Or more accurately looking at the history for the template  
> for that section [1], the original conversion stated:
> "{{{maxspeed:desc|Maximum speed, country-specific units}}"
> And the revision 3 minutes later changed it to
> "{{{maxspeed:desc|Maximum speed in km/h}}}"
> With a description for the edit (from Pieren) of
> "(restore metrics text, although it should be discussed)". I don’t  
> know where to find the versions pre 2008 to find out what it said on  
> older versions.
>
> I noticed that “should be discussed” note, but don’t know where to  
> look for that discussion. However, the decision to put in km/h has  
> made a mess of the maxspeed tagging on UK roads, especially as there  
> is both a conversion table in the wiki quoting whole numbers, and a  
> multiplication factor to use. See for example Tagwatch [2] where the  
> most common maxspeed is 48, followed by 30mph (the format I’ve been  
> using), and lower down come 48.28, 48.28032, 48.27808 and 48.3. I’d  
> also guess that the ways tagged as maxspeed=30 mean 30mph. If we had  
> stayed with assumed country-specific units then the tagging would  
> have been more consistent, easier for the user to tag, and not  
> require a conversion to a random number of decimal places.
>
> The maplint mention in the message subject is because Map Features  
> defines the value for the maxspeed key as being a number, so any way  
> I’ve tagged as =30mph, 20mph, 10mph, national or 40mph (as I did for  
> the first time yesterday) gets highlighted in the maplint  
> information, rendering it (no pun intended) next to useless for  
> checking other mistakes I may have made in the tagging.
>
> I have no suggestion what to do about either of these situations  
> though. I wouldn’t have been bothered at all if maplint hadn’t  
> suddenly started highlighting lots of ways in the area… I realise  
> that that is down to the word number in the wiki page causing the  
> validation to fail with the mph in the value.
>
> Thinking about it I have a similar issue with maxheight. Most of the  
> signs these days I think quote in metres, but I tagged one the other  
> day as so many feet and inches (possibly 13’9” – I forget), as I tag  
> what is on the sign and not what a metric conversion is (to the  
> centimetre, metre, decimetre, millimetre?). It seems I’m not the  
> only one [3].
>
> I suspect what I’d like most would be for maplint to recognise that  
> if the value contains valid units for whatever the key is (optional  
> units), then it wouldn’t highlight the way as in need of checking. I  
> believe maplint is common to both Mapnik and Osmarender (as it’s  
> highlighting ways on Mapnik which don’t yet show as I only added  
> them yesterday), and I know how to rebuild the not-in-map_features  
> information as I did it recently to add some keys that *were* in Map  
> Features but not being recognised by the T at H client when it  
> generated the maplint tiles, but it would probably need the perl  
> code that creates the XML tweaking to cope with optional units in  
> some way (a bit like it currently doesn’t like * in the value  
> column, IIRC, or “User Defined”).
>
> It’s raining here incidentally, which is why I thought I’d rant on  
> email instead of going out mapping a bit more of the area.
>
> Ed
>
> [1] http://wiki.openstreetmap.org/index.php?title=Template%3AMap_Features%3Arestrictions&diff=73032&oldid=73031
> [2] http://tagwatch.stoecker.eu/Great_britain/En/ 
> keystats_maxspeed.html
> [3] http://tagwatch.stoecker.eu/Great_britain/En/keystats_maxheight.html
>
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