[OSM-talk] re-using segments

[Matt Williams]

On Saturday 05 January 2008 16:08:40 Karl Newman wrote:
> On Jan 5, 2008 2:24 AM, Karl Eichwalder <ke at gnu.franken.de> wrote:
> > >> Am I btw correct in thinking that with the new three-layered way of
> > >> tagging things (nodes-ways-relations) that it's best to have split
> > >> ways on every node where another way meets it? So, instead of one big
> > >> way long as I used to tag things, now a separate way between every
> > >> crossroad?
> > >
> > > I hope that's not being encouraged. Ways should not be split just
> > > because there's an intersection. Ways should be split only when the
> > > properties of the way change (i.e., speed limit changes, or way goes
> > > over a bridge, etc.). Having lots of little streets is almost like
> > > having segments again. It's not very efficient.
> >
> > It depends.  If you agree to split streets because of bridges or
> > speed limit changes, you should also allow splitting because of
> > routes.  Take into account that speed limits are often useful for
> > fuel powered vehicles.
>
> Splitting ways for a route seems to be necessary. I was primarily
> objecting to splitting the way at every intersection, for no other
> reason than it's an intersection. But this trend of splitting ways is
> troubling. In the degenerate case, ways become what segments were.
> Split ways are much harder to maintain than one long way. Maybe we
> should consider a method of tagging sub-sections of a way (i.e., this
> route is part of that way from node A to node B), although I know that
> has its own problems.

Would it not rather make sense to group these separate ways (which are 
actually part of the same physical road, but different 'routes') with a 
relation such as 
http://wiki.openstreetmap.org/index.php/Relations/Proposed/Collected_Ways. 
Admitedly, this is almost paving the way for a repeat of the segment/way 
scenario with a way/relation scenario but I don't think that it's that bad; a 
way can belong to many relations. This would make requesting a 'road' from 
the database easy, just get all ways which belong to the 'road' relation; or 
if you want a bus route, just request that relation.

This would avoid the maintenance headache since any properties which belong to 
the whole 'road' could sit in the 'road' relation and so you wouldn't have to 
keep all the separate ways in sync.

Regards,
Matt Williams