The API is a composite index divided into five different categories of impact ranging from Good to Hazardous. Each category is equivalent to 100 points. The calculated index value may exceed 500 points, thus it is possible to add a sixth category. The HI used in the map compiled by NASA indicates the cumulative amount of haze from the beginning of September to mid-November 1997. The scale ranges from 1 (low pollution) to 6 (very high pollution). A matching of the two indices is shown in TABLE 5.1.