[Tagging] PTv2 public_transport=stop_position for stop positions that vary based on train length

Andy Townsend ajt1047 at gmail.com
Sat Aug 8 00:54:18 UTC 2020


Hello,

This is a question that actually arose out of a "how to tag" argument 
that's come to the attention of the DWG in the USA, but it's actually 
easy to describe in terms of data in the UK that I'm familiar with, so 
I'll do that.

https://www.openstreetmap.org/node/12004813 is a 
"public_transport=stop_position" for a local station and is part of 
https://www.openstreetmap.org/relation/6396491 among other relations.  
The problem is that train lengths vary, and there are a number of stop 
positions, each of which are actually signed on the platform for the 
benefit of the drivers.  From memory I think that there's at least a 
2-car stop, a 4 car stop and 6/8 and 10/12 car stops.  The problem is 
that the current node doesn't correspond to any of them.

As I asked on the changeset that added the one above 
https://www.openstreetmap.org/changeset/40603523 , how should these be 
mapped and how should the PTv2 relations be set up for the different 
services that use them, given that different train services will use 
different stop locations here depending on train length?  Should each 
stop position be mapped and should there therefore be different copies 
of each relation for all the possible train lengths?  Should a "pretend" 
average stop position be added which is actually never correct but will 
at least look nice to data consumers that use PTv2 data?  Given that we 
don't know the actual stop position perhaps the railway=station object 
(in this case https://www.openstreetmap.org/node/7154300845 ) should be 
used instead?

Maybe the public_transport=stop position should be omitted entirely?  
This last option seems extreme, but one reading of 
https://wiki.openstreetmap.org/wiki/Tag:public_transport%3Dstop_position 
where it says "However, marking the stop position adds no information 
whatsoever when it is placed on the road at the point closest to 
highway=bus_stop or on the tram tracks closest to railway=tram_stop. In 
that case it can be abandoned. " might actually support that (and that 
seems to be the view of one side of the argument in the USA).

Maybe the "correct" answer is none of the above?  With a "local mapper" 
hat on I've managed to avoid PTv2 since it basically isn't relevant 
anywhere I normally map things, largely because I don't tend to do that 
near any actual public transport infrastructure, but with a DWG hat on I 
haven't been able to avoid the question, hence me asking here.

Best Regards,
Andy




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