The Subway Map War of 1978 (theverge.com)

This article needs a graphic that compares the two competing maps side by side.

Of course, sometimes the decision is easy because you're bumping up against complexity limits to such a degree that you just can't fit any geographical reality on a map and still have something even remotely readable:

http://www.meik.jp/2rosenzu/jpg_640/tkyo_yko_chba.jpg

Why on earth would you write this article without an example of the Vignelli map?

http://nycsubway.org.s3.amazonaws.com/images/maps/system_197...

If anyone can name a better example of why you shouldn't simply trust designers to design something that needs to be useful, I would be interested to hear it.