[Tagging] traffic_signals:direction=* vs. direction=*

LeTopographeFou letopographefou at gmail.com
Mon Mar 20 17:46:17 UTC 2017

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
 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.



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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