Each state's population is represented as a "target" with the center circle representing the number of residents with normal Body Mass Index (BMI < 24.9), the middle ring representing the overweight population (25.0 < BMI < 29.9), and the outside ring representing the obese population (30.0 < BMI). The area of the entire target corresponds to the overall population of the state.
Source:
National Center for Chronic Disease Prevention and Health Promotion