On a node, traffic_signals:direction=* applies only to the traffic
signals while direction=* applies to all other tags which may be
associated with a direction (camera...). This is the additional meaning.
Let say that traffic_signals:direction=* is a more explicit tag than
direction=* (see https://wiki.openstreetmap.org/wiki/Namespace).
So why is there such a gap in use of the two keys between stop, give
ways and traffic lights? For me several reasons:
1. Because of the wiki. Some people (including me) look at the wiki as
guidelines when mapping (not only as a documentation):
1. https://wiki.openstreetmap.org/wiki/Tag:highway%3Dtraffic_signals
encourages traffic_signals:direction=* (even in the talk page)
2. https://wiki.openstreetmap.org/wiki/Tag:highway%3Dstop
encourages direction=*
3. https://wiki.openstreetmap.org/wiki/Tag:highway%3Dgive_way
encourages direction=*
2. Because editors use it that way... probably because they have
implemented directions following the wiki! But also because they
have implemented it for traffic lights, stops and give ways at
different point in time (and iD for instance don't support direction
for all of those features) and by different developers (and
different point of view). When you see a field in iD (for instance),
you often want to fill it when you know the answer. When you don't
see it, you may not think to create the tag by yourself (or maybe
not even know a tag exists).
3. Some quality assurance tools (such as Osmose) encourage (or have
encouraged) one form over another one, sometimes involuntarily.
4. In real life a traffic light is more often associated to another
device such as a camera, a pedestrian light... than stop signs which
stands generally on their own. So direction=* might be enought for
stops and give_ways most of the time for most of the mappers and
editors.
5. Maybe massive edits or imports have dug the gap.
I think that both stop, give way and traffic signals shall have a
consistent definition of direction and shall be consistent in which key
to encourage. As soon as direction=* is valid I would encourage it as
the primary method, would not deprecate the second one but explain it is
one way of avoiding ambiguities in some cases.
Yours,
LeTopographeFou
Le 20/03/2017 à 17:19, Jean-Marc Liotier a écrit :
traffic_signals:direction=* is used on 27278 highway=traffic_signals
objects:
https://taginfo.openstreetmap.org/tags/highway=traffic_signals#combinations
highway=stop is combined with a direction tag on about 77000 objects
(direction=backward, direction=forward and the literal direction=*)
https://taginfo.openstreetmap.org/tags/highway=stop#combinations
highway=give_way is combined with a direction tag on about 43000 objects
(direction=backward, direction=forward and the literal direction=*)
https://taginfo.openstreetmap.org/tags/highway=give_way#combinations
Given how widely used the direction tag is for highway=* signs, why
isn't it also applied to highway=traffic_signals ? Does
traffic_signals:direction=* bear additional meaning that direction=*
does not convey ?
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