[Tagging] Relation for saying "x is attached to y"?

[Peter Wendorff]

  On 04.09.2010 07:00, Steve Bennett wrote:
> Any existing renderer would not render C at all. Any renderer (or
> other tool) that added support for railway=train_line, would
> presumably also add support for the relation.
>
As that's right from the applications point of view, keep in mind the 
need for mapping people.
Artificial, virtual lines like these are good for the renderers - but 
complicated in editor software: I have
1) to know about the train_line concept
2) to move this way additionally

I'm sure, there has to be a way for renderers to collapse parallel ways 
to one - without explicit tagging in the database.
The railway example is only one of more examples.

If collapsing takes into account the number of collapsed tracks to 
consider it for the signature in the map - even better.

regards
Peter