Neighborhoods in the same city can differ in temperature by as much as 20°F, due to differences in tree cover and other factors that influence the intensity of the urban heat island effect. To learn where action is needed to protect disproportionately affected populations now and in the future, the interagency National Integrated Heat Health Information System (NIHHIS, led by NOAA and the CDC) and partner CAPA Strategies LLC launched community-led urban heat island campaigns that map the hottest parts of cities. Through this program, NIHHIS works with communities to inform equitable heat resilience solutions based on campaign results. Citizen scientists from each community collect temperature and humidity data in their neighborhoods, helping to increase awareness of the health risks of heat within each community. As of 2021, 24 communities across the country and internationally have mapped their urban heat islands. Data from the program have been used in a variety of ways, including to support tree planting strategies, installation of pavement that absorbs less heat, educational efforts, and more. All data reports are open source and available on Heat.gov.