[OSM-talk] [Tagging] - RFC - Motorway_link implies oneway=??

[Ben Laenen]

On Thursday 02 October 2008, Alex Mauer wrote:
> Matthias Julius wrote:
> > I don't.  I think it follows the "principle of least surprise"
> > better if implied values don't change too much.
>
> Great, then we should leave this as-is (implied oneway=yes for
> motorway_link)

That would work if it weren't for the fact that 
http://wiki.openstreetmap.org/index.php/Tag%3Ahighway%3Dmotorway_link 
didn't imply oneway=yes until some months ago. The page actually said 
that oneway=yes was _not_ implied in its example, and mentioned it as 
one of the extra tags for further information.

> There are three options:
> 1. make no assumptions: This means every single motorway_link needs
> to have a oneway=yes or oneway=no (or oneway=-1).  A pain for
> taggers, and doesn't help makers of routing applications who still
> need to handle the case where there is no oneway tag.

Given the changing implication of oneway=yes this is actually the only 
option left -- like it or not, painful or not -- since they could be 
added by people who read that it was implied and by people who read it 
wasn't.

Only if all motorway links have a oneway tag we can have an implied 
value for oneway, so we know that from that point the rules were clear 
and the OSM data should be correct according to that implication (if 
you can somehow communicate that to all our mappers so they all know 
it).

Ben