To do these kinds of nature and human health studies, researchers need maps of how green an area is and surveys or medical records on how healthy its constituents are. This data isn’t as readily available in poor and developing nations that don’t have reputable health care records or on-the-ground green space surveys, so these countries—and their citizens—are often left out of the conversation.
To bring more people into the fold, an international team of researchers gathered satellite imagery from 90 large cities in 60 countries spread out across the Middle East, Central America, South America, and Southeast Asia, as well as North America, Europe, and Australia. Taken during the summer, these overhead images gave the team a good sense of the green vegetation of every city relative to its population.
Next, the team compared this to each city’s average happiness score, as reported in the United Nations’ World Happiness Report, a standardized report that asks people around the world to rate their life satisfaction on a scale of 1 to 10. They also factored in every city’s wealth, as measured by its GDP, to see how that might affect the happiness of its citizens.