[OSM-talk] two highways use the same way

[Dermot McNally]

2008/6/20 Rory McCann <rory at technomancy.org>:

> Personally I think it'd be good to tag the road as primary *and*
> secondary, i.e. that we should have 'highway=primary;secondary'. This
> makes it possible to see how many km of secondary roads there are in an
> area, or to highlight only road 172.
>
> *However* most of the renderers can't deal with semi-colons well. Just
> see Dermot McNally's post in late May about "Potlatch and the evil
> semicolons". I don't really like mapping for the renderer though. :)

Well, this is all going to be heavily dependent on the local
conditions. In Ireland, for example, roads just plain don't multiplex.
In cases where, say, the route of the R300 Regional road travels for
2km on the N45 National road, the legal instrument defining the R300
will "stop" the road for that 2km and resume it on the other side.

Other countries (Germany, I believe and the US) do allow for this.
Mapping for the renderer is certainly evil, but unless somebody wants
to propose coloured stripes, we only ever expect to see the road
rendered in the style of the higher classification. Today, a road
tagged "highway=trunk; primary" will not be rendered at all, and this
fact alone convinces me that it's a bad idea to do so (today). If
renderers can be instructed to render as per the highest
classification, then I'd consider it valid to tag in that way. But
only in cases where the road is a true multiplex, carrying two route
numbers and two parallel classifications. It still won't be valid to
do this in Ireland.

Dermot

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