This is so cool. A software firm used General Transit Feed Specification (GTFS) data to visualize all the CTA buses for an entire day (via The Atlantic Cities). If you make the video full screen, you can make out the El lines, which are in color.

By comparison, here's New York; the density of public transportation there is just mind-boggling:

The pattern of D.C.'s public transportation is wildly complex:

As is Philadelphia's: