There are a lot of different ways to measure the relative "greenness" of a given city. 
 
 You can look the energy efficiency of its buildings, the average carbon footprint of its citizens or even the number or people who have "An Inconvenient Truth" in their Netflix queue. 
 
 The people behind event finding app Gravy, on the other hand, used a different measure in determining their list of the greenest cities in America--the number of "green-friendly" events happening in a given year. 
 
 Does a critical mass of self-congratulatory "awareness building" festivals necessarily translate into a city and its citizens making serious strides toward protecting the Earth? 
 
 Of course not. But looking at the overall number of events does yield a pretty good idea of a city's level of publicly stated commitment to environmentalism, which often results in action. So it's not exactly surprising that the cities sitting atop Gravy's list for hosting the most environmentally-themed events also tend to cluster near the top of rankings of greenest cities based on other metrics. 
 
 Check out this list of Gravy's five "Most Earth-Friendly Cities" that comes complete with a unique Earth Day activity for each city: 
 
 Most Earth-Friendly Cities ||||| Starting in 1996, Alexa Internet has been donating their crawl data to the Internet Archive. Flowing in every day, these data are added to the Wayback Machine after an embargo period.
– You can measure the green-friendliness of a city in many ways—like its average carbon footprint per citizen or the energy efficiency of buildings. But the event-finding app Gravy has decided to measure cities by the number of pro-environmental events each one hosts in a year, the Huffington Post reports. Is this an official barometer? Hardly, but it does reflect people's interest in the green movement. Here are the top five US cities, each with a unique Earth Day activity: Portland: Operation Clean Street San Francisco: Earth Day SF Boston: Earth Day Massive Spin Jam Austin: Annual Earth Day Festival Chicago: Chicago Earth Day 5K Click for more.