[OSM-talk] [Tagging] - RFC - Motorway_link implies oneway=??
hawke at hawkesnest.net
Thu Oct 2 19:35:17 BST 2008
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
>If a highway is not oneway
>by definition oneway=yes should not be implied.
You do realize that "implies" means "if no value is specified, this
should be the value that is understood", right? That the actual tags
over-ride the implied value?
So "the implied value could be incorrect some of the time" is no reason
not to have an implied value. That's why it can be over-ridden by
applying the appropriate tag. Having the implication is about reducing
the effort required for someone to tag a motorway, and making it so that
consumers of OSM data can make assumptions about the data.
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.
2. Assume oneway=no. This means that 95+% of motorway_links must be
tagged. Still a pain for taggers. Makers of routing apps can't safely
make this assumption anyway for fear of routing someone the wrong way up
the motorway_link. It does mean that motorway_link has the same default
as the other highways except for motorway though.
3. Assume oneway=yes. This means only 5-% of motorway_links must be
tagged. It's the safe assumption that routers will have to make anyway.
And of course it doesn't prevent anyone who wants to from explicitly
specifying a oneway key/value for every motorway_link if they feel like
Looking at the above, assuming oneway=yes seems the only way to go. Am
I missing some big problem with it?
> Trunk roads are
> probably mostly oneway, too ...
Off-topic. This is about motorway_link.
-Alex Mauer "hawke"
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