Martin Koppenhoefer wrote:
Actually the "source:maxspeed" tag was discussed years ago (2009 IIRR)
on this list and by the time approved. The idea to use maxspeed:type
instead is very new compared to this, and there wasn't any actual
proposal to see whether this was backed by the community, rather then
what appears to be a national initiative of some folk in the british
comunity in order to make up something different to how it is done
elsewhere:
http://taginfo.openstreetmap.org/keys/maxspeed%3Atype#map
http://taginfo.openstreetmap.org/keys/source:maxspeed#map
... another interpretation as to what actually happened is that
"source:blah" was in widespread use since the beginning of time for "the
source of the blah key" (survey, local_knowledge, whatever). Then at
some point people decided to use "source:maxspeed" to refer to the zone
(e.g. if a road's in an urban area, and urban areas in your country have
a 30 km/h speed limit regardless of signage, then it's OK to say that
the "source of the maxspeed" is something like "DE:zone:30" or similar).
In the UK "maxspeed:type" is usually used with "national" speed limits,
not zone-based ones. The source of the maxspeed is therefore "survey",
"local_knowledge" or similar, and "maxspeed:type" is used to indicate
that it is a "national" maximum speed limit, not a numeric one. It's
important to record what the sign actually says, not just the number
that that sign happens to currently represent - historically the
national speed limit for different classes of road for cars has changed,
and it may again in the future.
There was (a couple of years ago) a significant usage of
"maxspeed=national" or similar in the UK. this caused a certain amount
of "toys being thrown out of prams" from people (mostly from countries
where the posted limit is always numeric) who expected the "maxspeed"
value to always be a number. The compromise was to store store the
actual posted sign value in maxspeed:type, and what number that happens
to currently correspond to in "maxspeed" (and the actual source, if it
needs to be stored, in maxspeed:source for compatibility with other
source keys).
Cheers,
Andy
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