[OSM-talk] Superways again

David Earl david at frankieandshadow.com
Fri Mar 16 16:31:59 GMT 2007

In view of the discussion on tagging junctions, I thought I'd raise this old
chestnut again under a separate thread.

There have been a number of discussions around abandoning segments
completely, arguing that ways would become simply a linear chain of nodes.
While I think most people agree there is merit in this, it has the enormous
disadvantage that it requires pretty much everything (editors, renderers,
utilities, ...) to be rewritten to accommodate such a change. Some of us
talked about it in passing in Oxford a couple of weeks ago. I think making
this change this would be unproductive.

However, the concept of adding a higher level structure on top of ways is, I
think, still desirable; at the same time requiring that Ways are what we
all, I think, now believe they should be and do conventionally, i.e.
contiguous, ordered, unidirectional, non-branching sets of segments.

Reiterating some of what's gone before:

There are then lots of advantages to grouping such ways.

* If you break a Way at a bridge, you can group the three Ways (either side
and the bridge itself) so their commonality (it's the same road) can be
represented (and so on along the road).

* An estate road with many branches can be represented as a whole.

* If you want to represent a bus route, the route tag in theory allows this,
but in practice you can't put more than one route on the same Way, so it
can't also be a different bus route or a cycle network route, and the route
isn't coherent in any useful way - you have to search for where it goes
next. So grouping ways to represent the concept of route would be helpful.
Note this means ways can belong to more than one superway.

* A non-roundabout and non-node junction could be represented (together with
its name or number) as a bag of ways (consider a grade separated single
carriageway with four slip roads, or a cloverleaf).

At the same time, we need the database api and ideally editors to enforce
(and naturally create without bothering the user) the stricter definition of
a Way, and prevent (all? some?) tags being put on segments. Ideally editors
would also suppress the visibility of segments to the user, even though they
are there underneath, as they are just 'glue' to hold the ways to the nodes.

Not much new in this message, but I want to light the match again.


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