Riding the subway as a kid it used to bother me that the MTA's map of the New York subway system distorted the underlying geography of the city so badly. But this cool graphic made by Peter Dovak to show a properly scaled map of WMATA's Metro system in the D.C. area shows that mass transit planners have a perfectly good reason for not doing this.
Dovak's map is interesting to look at and teaches us some useful things (I hadn't realized that the U-shape of the red line was so asymmetrical) but if you actually want to ride the system this map is terrible. You can't see where the downtown stations are, and there's tons and tons of wasted space out in the suburbs. The compression and distortion are very very necessary to create a viable system guide.