Look out your window. Can you see three trees? That's the opening query of the 3-30-300 test, an urban planning framework that has spread rapidly since Cecil Konijnendijk proposed it. The rule sets three minimum standards: three trees in view from every window, 30% neighborhood tree canopy, and a park within 300 meters. It's a straightforward benchmark for equal access to nature.

European cities have embraced the concept. Florence committed to planting 50,000 trees by 2030, while Fort Collins, Colorado formalized it as planning policy. Yet implementation lags far behind ambition. A study of 862 European cities reveals only 14% of residents meet all three criteria. Southern European cities perform worst - in Valencia, just one in ten people can see three trees from their window.

The health implications are measurable. Research shows people with tree views have better mental health, and hitting the 30% tree cover goal could prevent 2,644 heat deaths annually across Europe. However, one in three Europeans live in areas failing this standard. Among eight global cities tested, only Singapore passed completely.

Two European cities exceed the 50% threshold: Espoo, Finland and Varese, Italy. For the rest, the researchers' conclusion rings clear: Tear up the asphalt; plant trees. The standard isn't aspirational—it's a minimum that most cities currently fail to provide.