Because git doesn't allow cycles? Then as cool as this is (and it's very cool), perhaps this isn't an appropriate tool for this purpose.
Or might the natural, human-built cycles be expressable as subrepositories?
Would Mercurial be more appropriate, or do you think DVCS are simply not an ideal way of mapping metro lines?
As to Mercurial being better, I don't know but I doubt it.
My comment isn't even really directed at the appropriateness of DVCS specifically. It's just a general observation of using an acyclic tool to describe a network with cycles. We do that a lot, sometimes for play, sometimes for practicality, and sometimes because we just flip the fuckit bit. http://thechive.com/2009/11/11/there-i-fixed-it-23-photos/
That said, this is most likely just meant as a fun visualization, because the visualization does look like a railway map.
Isn't the sole reason this is on HN, on the frontpage, exactly the fact that git and it's graphs aren't appropriate at all for drawing metrolines and yet somebody though of it and then did it as well?
I don't think the tooling is made for it either.
> git commit-tree <tree> [(-p <parent>)...] < changelog