It's The Cities, Stupid

"Look at our famously blue West Coast. But for the cities--Seattle, Portland, San Francisco, Los Angeles, and San Diego--the West Coast would be a deep, dark red. The same is true for other nominally blue states. Illinois is almost entirely red--Chicago turns the state blue. Michigan is almost entirely red--Detroit, Lansing, Kalamazoo turn it blue. And on and on. What tips these states into the blue column? Their urban areas do, their big, populous counties.

...Liberals, progressives, and Democrats do not live in a country that stretches from the Atlantic to the Pacific, from Canada to Mexico. We live on a chain of islands. We are citizens of the Urban Archipelago, the United Cities of America."