Urban areas are often several degrees hotter than their surroundings, and planners have increasingly turned to tree planting to reduce this effect. Studying five neighborhoods in a large US city, a team of researchers concluded that tree canopy cover alone does not determine how hot a neighborhood becomes; the share of land covered by impervious surfaces such as asphalt and concrete also appears to matter. The table shows each neighborhood’s tree canopy cover, its share of impervious surface, and its mean summer afternoon surface temperature.