[Tagging] Self explanatory?

Martin Koppenhoefer dieterdreist at gmail.com
Mon Dec 10 16:10:14 GMT 2012

2012/12/10 Martin Vonwald <imagic.osm at gmail.com>:
>> I'd expect to see this represented by a way that goes straight and has
>> a crossing (or exit link) turning slightly to the right, instead in
>> the example it seems as if there is a "V"-crossing with the leftern
>> (straight) part more inclined than the actually turning one (link).
> If you draw the OSM way in the middle of the carriage way you can't
> draw a straight line here. If you don't draw the OSM way in the middle
> of the carriage way the rendering result will be wrong, because
> renderers assume that the OSM way is in the middle.

the rendering result will always be "wrong" if you look into these
details, you simply can't get it perfect without explicitly drawing
the area or maybe adding lots of lots of width information every few
cm (including information how the transition will be between those
widths: steady change or with "corners") ;-)
The question is which direction the inevitable compromise takes, and
IMHO it is desirable that straight roads remain straight, very similar
to situations where dual carriageways get to crossings (inside the
crossing area you usually don't have a dual carriageway, but rather
the two unify into one, still we don't model this because it would be
confusing and ugly). Very similar I see motorways, where I'd put the
highway-way on the center of the "main" way (if this is clear, usually
should be the one going straight) and not on the center of all lanes
(I wouldn't include turning lanes).

>> As for your triangles: if we should choose to represent these
>> situations (bifurcations of carriageways) in a way similar to these
>> examples they should still not be areas (or closed ways).
> What options do we have?
> * Tag only the nodes. This would be near to invisible even if the
> editors would show those nodes more prominent and for the consumers if
> would be harder to use (I guess).
> * Use a relation and put all the nodes into it. I thought about a
> minute what I should write here... I decided to only write this:
> relation! ;-)
> * Connect all the involved nodes with a way. Good visible in all
> current editors without any change. The consumers should be able to
> interpret this more easily compared to the nodes-only solution.
> That's why I went for the way. Closed or not doesn't really matter here.

I'm fine for the "virtual" way (thus not needed IMHO), but in your
examples there are triangles (areas) which are even stranger IMHO.
There is still the possibility to use a relation to combine actual
lanes (not tagged as highway but as lanes), e.g. the area relation.


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