This link compares the relative extent of subway systems over the world. What would be even more interesting would be a comparison of which subway system stinks the most. I have transited on many of these subways, and plan on hitting the rest of them before I expire.
http://www.fakeisthenewreal.org/subway/
A couple of interesting ones that I have been on although the scale of the Paris one seems off, although it is purported to scale.
New York
DC
Paris
Seoul
