This is a comprehensive indicator of the impacts of temperature and humidity on the human body. It reflects the degree of comfort sensed by human bodies at a certain temperature and humidity. The index is a combination of temperature and humidity and has the formula DI = T – (0.55–0.55 f) (T – 58), where T = temperature, and f = relative humidity. In general, the index can be categorised into 11 classes: −6: extremely cold, −5: exceptionally cold, −4: very cold, −3: cold, −2: slightly cold, −1: cool, 0: comfortable, +1: warm, +2a: hot, +2b: sultry, +3: very hot. This index is one of the key evaluation indicators of the quality of a tourist site.