The most familiar type of city map also happens to be one of the most geographically inaccurate. Perhaps it is that delectable paradox that makes the common subway map so enjoyable to study. Or maybe it's the subway map's perplexing and sometimes dysfunctional marriage of form and function, its combination of color and shape to move us around our cities, or simply its sheer beauty as an icon of our urban environment. Below, a compilation of the very best official designs (click each image for a full-size map.)
As Mark Ovenden notes in his fantastic Transit Maps of the World, it was Harry Beck's innovative 1933 design for the London Underground that freed subway map designers to take poetic license, simplifying routes, stretching and compressing distances (for a sense of scale, compare these diagrams of the world's subway systems; Paris' Metro may seem as big as London's Underground, but it's a fraction of the size.)
Other cities have sought to innovate, but the best maps, like Beck's design, transform the shapes of the sprawling steel behemoths beneath us into both a visual aid and a sort of quotidian artwork, as helpful as they are fun. Even while websites like Google Maps and Hopstop shift our relationship to these maps, they remain essential to our life in the city, ideograms in a language we're always learning.
UPDATE: Wanda Wanders also wrote about the best subway maps, with ratings.
More on Subways at TreeHugger
Design Makes a Difference: Frank Pick in London
Promoting Public Transit: I Heart This Subway Map!
Navigate Subways Faster With Augmented Reality Map
The Coolest Subways in the World (A Slideshow)
Subway Systems of the World