Submitted by Pablo Martin, who says:

This is the Madrid metro map from 1945, I found the diagram below really interesting, as I haven’t seen a similar one for any other network.

Transit Maps says:

Nice find, Pablo! The geographical map is fairly clumsy and unremarkable, but the diagram beneath is very interesting. It’s what I call a “linear diagram” – each route is shown as a straight line, with interchanges indicated by a vertical joining line or bar. It’s not entirely unique (see this more recent example from St. Petersburg), but it’s not a form that’s ever been very popular. It only really works for relatively simple networks with a few clearly defined interchanges… Madrid’s four short lines at the time made it a perfect candidate for such a diagram.