However, the country's other regions receive equal representation in the ranking that also considers the amount of parks per 10,000 residents, as well as the percentage of the population that walks, bikes, carpools, takes public transit to work or works from home.
Here's what the site had to say about its top selection, Madison, WI:
"Madison earns the distinction of being the greenest city in the U.S., partly due to the fact that the city is literally "green"—its 12.7 parks per 10,000 residents is the highest mark of all cities in the country. The Madison area is home to over 15,000 acres of lakes and more than 200 miles of biking and hiking trails. In fact, the city boasts more bikes than cars, which no doubt contributes to the area's great air quality."