[ccalloway]

What if the longest distance meant "longest shortest rail distance between two points".

Ie, the longest track distance between any two places on Earth, subject to the constraint that there is no shorter train journey between those two points.

This seems to me to be a much more logical, and also more interesting, interpretation of the question than the one used in the article.

[Chris2048]

Wouldn't that simply be the "shortest rail distance between two points"?

[ExtraE]

Not exactly. Parent is describing the graph diameter [1].

[1]- https://mathworld.wolfram.com/GraphDiameter.html

[ccalloway]

Well, no. The shortest rail distance between two points is very very short, because you can choose the two points very close to one another.

[Chris2048]

Oh, right. Fair enough. The two points with the longest shortest-path, with no fixed choice of points.