Obesity is more common in low-income areas. Why? It may seem intuitively obvious that lack of adequate income, transportation, cooking facilities, supermarkets, and opportunities for physical activity would make it difficult for people to eat healthfully and be active, but inituition is one thing and evidence is another. My NYU colleagues Jennifer Black and James Macinko now provide the evidence in a most useful review paper. Want to improve the “built environment”? This is a great starting place.