# [Tagging] roundtrip

Johnparis okosm at johnfreed.com
Fri May 25 13:53:40 UTC 2018

```I would generally agree with all your points.

A slightly more formal definition (though not fully rigorous) for me would
be: a circular route is one in which, from any boarding area, you can

I say boarding area rather than point because of the fairly frequent case
where the dropoff and pickup points serve the same area (such as a train
station) but are not necessarily identical.

The example I gave in the other thread, I believe, is marketed that way
because people are indeed supposed to leave the bus, though I would imagine
that since most people use weekly or monthly passes, most drivers would
probably look the other way.

https://www.openstreetmap.org/relation/8140184

Thorsten's description is good, but technically pretty much any bus route
is a roundtrip (circular) topologically. A typical route is:

A -> B -> C -> (forced disembark) -> C' -> B' -> A' -> (forced disembark)
-> A ...

Typically B and B' are on opposite sides of a two-way street. That's the
simplest example. Topologically it's the same as a circular route, because
the bus makes a U turn at each end and continues. So it's a question of
marketing and general public understanding, more than mathematical rigor.
But the variations are bewildering.

Personally, I track circular routes for validation purposes. As I
understand Public Transport version 2, every route variant requires a route
master, even if the master has only one variant. So masters with one
variant are oddballs; most routes have at least two. A master with only one
variant is typically either (a) a circular route (so I mark them in my
private database), (b) a PTv1 route (thus needing an upgrade), or (c) an
error (thus needing further investigation).

I would mark the OSM example above in my data as a circular route, so I
won't flag it as needing further work, but it would not meet my more formal
definition of a circular route, because of the forced disembark, so I would
not consider it as qualifying for a "roundtrip=yes" tag.

If there is sentiment to change the name of the tag, I would suggest
"route:circular=yes". (There are "only" 25000 in the OSM data, so it might
be manageable.) I don't like "circular=yes" because it's so vague.
(example: building=silo circular=yes ?)

On Fri, May 25, 2018 at 1:23 PM, Peter Elderson <pelderson at gmail.com> wrote:

> Oops, I didn't think this topic would generate so much response, even
> though I charged a bit in the first mail.
>
> Let me try to make some sense of it. I have seen enough use cases, I think.
>
> a. There are two use cases which use the actual definition on the wiki: a
> geagraphically closed route, start-point=end-point. One is about marking
> routes as roundtrips based on JOSM validation, then monitoring if the chain
> had broken so you can fix it. The other is marking an unfinished  route as
> roundtrip in order to detect it for completion. To me, this is almost the
> same use case.
>
> b. A range of use cases are opposite: a geographical roundtrip has to be
> regarded as non-roundtrip, or a geographical non-roundtrip has to be
> regarded as a roundtrip anyway.
>
> Could we agree that the wiki should cover b.?
> I think this does not exclude a.
>
> If anyone judges that a geographical roundtrip should explicitly be tagged
> as roundtrip=yes, ok.
>  do think that when one of the use cases under b. applies, then you have
> an exception to what the map says, with a reason. Then this takes
> precedence over the geographical default.
> This could be a geographical roundtrip tagged as roundtrip=no for whatever
> reason, or a geographical non-roundtrip tagged as roundtrip=yes, for
> whatever reason. It would be nice to know the reason, of course. For my
> part, "everybody/nobody here calls this a circular line" is reason enough.
>
> Could we agree on that too?
>
> If so, all that remains is add this to the wiki.
>
> --
> Vr gr Peter Elderson
>
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>
>
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