Why does a loop make it impossible to sort the ways? It implies that a
section of the route is present twice in the relation, but there is
surely no distinction between the first traversal of a way and the
second traversal?
On 2018-05-03 18:42, Volker Schmidt wrote:
> I will try to explain this in a more systematic way:
>
> Routes belong to either of two categories: (A) Those whose members can be
> sorted into a single ordered sequence (B) Those that cannot be sorted into a
> single ordered sequence of members Sorting makes only sense for category (A)
> Routes of type (B) can be subdivided into routes of type (A), each of which
> can be sorted, but the overall route can not be sorted.
>
> Routes are of type (A) if
> (1) the path from begin to end is identical to the reverse path with all
> members traversed in the reverse order and in the opposite direction
> or
> (2) all members have the role forward
> or
> (3) all members have the role backward
>
> Any route
> (1) that has more than two ends
> or
> (2) that contains any loop (except the case that the entire route is a single
> loop)
> or
> (3) that contains any element with role forword or role backward (except the
> cases of all-forward or all-backward)
> or
> (4) that contains node or area elements
> is of type B
>
> I am not sure if I have taken care of all cases - please complete as
> necessary
>
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