A city's tree canopy cover is the amount of its land covered by leaves, trees, and stems when viewed from above. It can be calculated to a percentage, and Boston's canopy (around 29%) is higher than the national average — as well as that of New York City, Philadelphia, Chicago, and San Francisco.
Boston has also started an campaign – Grow Boston Greener – which aims to grow the canopy cover to 35%. The initiative, launched in 2007, will help plant 100,000 new trees in the city by 2020.
The You Are Here project publishes one unique digital map every day. You can view their first six Cambridge maps online, including an interactive look at the city's street greenery.