[Tagging] Status of oneway=cw oneway=ccw

Kevin Kenny kevin.b.kenny at gmail.com
Thu Mar 14 14:39:59 UTC 2019


On Thu, Mar 14, 2019 at 6:45 AM Sarah Hoffmann <lonvia at denofr.de> wrote:
> I was pointed to the discussion from the waymarkedtrails issue
> tracker. I haven't followed the whole discussion. Here's just my
> two cents as somebody how processes route data.

I know that you and I have pretty strong disagreements on the
processing of route data (mostly owing, I think, to the ridiculously
high number of route concurrences in the US), but on this specific
issue, I think we're in 'violent agreement'.

oneway=* definitely goes on the relation, not on the member ways, for
the case where a route runs only one way by convention, but the
individual ways can be followed in either direction, physically and
legally.

The order of ways in the relation definitely determines the direction
to which oneway=* refers. It oneway=yes or oneway=signed (or whatever
we settle on) is present, the ways are traversed from the first
relation member to last - irrespective of the direction of the way.

I'm aware of what 'forward' and 'backward' are intended to mean - it's
there to handle cases like a pair of one-way streets that belong to
the same numbered route, or the two ways of a dual carriageway. When I
suggested borrowing this tagging for the one-way route, I thought it
was Mostly Harmless to do so, because in this case, the way only
exists in one direction. Navigation engines honor the 'forward' and
'backward' values (to avoid sending you on the wrong direction of a
route - some routes separate into 'forward' and 'backward' on two-way
streets, to avoid illegal turns or something), and so I thought that
the explicit direction would be a little extra level of safety against
misrouting. It doesn't exactly misinform, because as I said, the route
doesn't exist in the opposite direction.

I concede that nearly everything can work without the explicit
'forward' and 'backward' indicating whether the route runs with or
against the direction of the way.

I think we both agree that oneway=cw and oneway=ccw are difficult for
both navigation and rendering, and hope we can lay those to rest.



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