[OSM-talk] The segments vs ways vs superways question, , again...

[Ed Davies]

Dave wrote:
> No, ways are ordered lists of segments...

Correct, in the technical sense that the ordering of the segments
in a way should be preserved.

http://wiki.openstreetmap.org/index.php/REST says:
> A 'way' is an ordered list of segments.

(Pity it uses the word "list" though, "set" would remove the
possibility of a segment appearing twice.)

Dave went on to write:
> what order is another matter
> entirely, so misordered would be correct in terms of some expected order...
> although it's entirely possibe the creator would disagree over whether it
> was in fact misordered.

Again correct - the ordering means whatever the creator meant it to
mean.  My reading is that the ordering of segments in a way is just
a convenience for access - for example, the order is preserved if
you upload a way then download it again to continue editing.  It
really doesn't follow that the ordering of the segments in the way
is how they are connected on the ground, or even imply that they
are connected (though I suspect disjoint graphs are not a brilliant
idea if you want nice rendering of labels, etc).

http://wiki.openstreetmap.org/index.php/Data_Primitives says:
> A way is a list of line segments that describe a street, or similar. 
> The way can be in any form, and segments can be members of other ways.

In the absence of any clarification I think the words "any form"
licence disorderly spaghetti monsters.  It's up to the renders to
deal with that.

Allowing arbitrary segment sets (lists) certainly makes editing
easier.

Ed.