tl;dr: The 3-30-300 rule, proposed by Cecil Konijnendijk and adopted by cities like Florence and Fort Collins, states every home should have a view of 3 trees, 30% neighborhood tree canopy, and a park within 300m. A study of 862 European cities found only 14% of residents meet all three criteria, with the 30% canopy requirement being the hardest to satisfy. Globally, of eight major cities tested, only Singapore passed — a problem with real consequences, since hitting the 30% target alone could prevent thousands of European heat deaths annually.