For PT, roundtrip is not an attribute of the route, it's a type of ticket or 
it's what you use the transport for. You can do a roundtrip on a circular line, 
but also on non-circular lines or mostly non-circular with a loop at the end, 
whatever. To express that a PT route is circular, I think the term circular 
would be better than roundtrip. 

For hiking|foot routes, exception is the rule when it comes to branches, 
alternatives, excursions, approaches and shortcuts. For me roundtrip on a 
walking route relation means: when you keep following the main route markings, 
it takes you back to where you begun. This does not exclude any alternatives, 
such as optional extra loops or a common approach/exit route at a starting 
point. Only roundtrip=yes is needed here, if not present assume it's not a 
roundtrip. Note that many trails consist of a number of linear routes, together 
making for a roundtrip. I tag roundtrip=yes only on the parent route relation. 
Loop or circular would also be just fine, but I see no reason to change 
existing tagging here.

Question: who wants to know if a route is a circular route/loop/roundtrip? Is 
it the map user? No, (s)he can see it on the map. Is it important for routing 
and navigation? I can't see how, but there are experts on this list who know 
more about this. So far I know of only one application: 
categorisation/filtering of trips in order to present the user a choice between 
roundtrip walks or linear walks. The roundtrips were actually meant to be 
daytrips, and linear walks were to be presented as " long distance walks", but 
a separate category long distance roundtrips could be deducted from the data, I 
guess.

Question: who wants to know if a route is actually a closed loop without any 
branches?
What do you need this information for? So far, I know one application: if a 
route is tagged as a closed loop, e.g. with closed_loop=yes, and it's not 
complete or interrupted somewhere, you can detect that with a checking tool. It 
would be a sort of fixme, then. Most routes I maintain would not profit from 
that. 


FrGr Peter Elderson

> Op 21 dec. 2019 om 15:31 heeft marc marc <marc_marc_...@hotmail.com> het 
> volgende geschreven:
> 
> I always thought that routrip=yes was an alternative when there is no
> start and end point to enter in from=* to=* key.
> Otherwise circular routes with a known start/end point can enter
> as from=A via=B to=A.
> _______________________________________________
> Tagging mailing list
> Tagging@openstreetmap.org
> https://lists.openstreetmap.org/listinfo/tagging

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