[OSM-talk] Zonal restrictions.

[Ben Laenen]

On Thursday 14 May 2009, MP wrote:
> > Except it's not a geographic area, but rather a set of streets with
> > that restriction. If a bridge or tunnel without the restriction
> > goes over/under a street with the restriction you'll have a
> > problem.
>
> In that case, that bridge can have differen speed limits set directly
> on the way. Just define that tags on individual ways override tags
> set in the zone and this will solve the issue.
>
> > So while it may work for many zonal restrictions to use an area
> >  (although even then there are still issues) you need another way
> > as well due to the bridge/tunnel issue, and that other mehod can
> > only be relations.
>
> I've seen many zones with some limitations (mostly speed limit or
> some parking limitations), but such zones rarely contain any bridges
> or tunnels. If they do, they can be either tagged individually, or we
> can also make new relation that will contain the zone and roads that
> are NOT in the zone (relation containing those few exceptions like
> the bridges, tunnels, etc ... so they won't need individual tagging)

And who's going to think about that? You're not exactly making it easy 
for a mapper if he or she has to know about features you're not able to 
see on the road he has just explored...

I'd suggest one should tag a road with features found on that road and 
not with features that are missing on the road.

And these situations are more common than you may think. Built-up areas 
are the most common where such a thing happens here as they're of 
course the largest kind of zonal restrictions, and each city will have 
it's roads crossing them without being part of it. But I've also seen 
it with zones with parking restrictions or zones with speed 
restrictions.

And you just can't tag the road with for example an overruling maxspeed 
tag, as the road may just have its default maxspeed in which case you 
don't tag that speed.

Ben