[OSM-talk] Topology (was: OSM the mediocre alternative)

[Schuyler Erle]

* On 27-Apr-2007 at  2:28AM PDT, Frederik Ramm said:
> 
> >Do you have any examples that don't involve a difference in altitude
> >or z-index? I can't think of one. :-/
>
> But thinking this further, you end up at the very  same point I
> postulated, that you cannot simply assume that two  things meeting
> somewhere in lat/lon do actually meet logically - in  my description
> you would have to explicitly select the object you are  dealing
> with, and in a layered world you would have to select the  layer.

I have thought very hard about this and I have to agree. The only
thing that OSM seems to concretely need topology for is modelling
connectivity of transport networks.

Topology introduces enormous complexity in spatial processing, and
will slow down storage and querying in a spatial database by at least
an order of magnitude, even with appropriate caching. With that in
mind, I wonder if it wouldn't make more sense to store feature
geometries as simple geometries, but continue to represent transport
network intersections as separate objects (as OSM currently does).
This approach might make it possible or even easy to model attributes
of the intersection, such as turn restrictions and the like.

SDE