Online map of the occurrence ratio of disasters caused by natural disasters in China (1949-2000). Legend is disaster ratio, occurrence ratio,in terms of severity, the ratio from strong to weak is 0.12-0.37; 0.09-0.12; 0.07-0.09; 0.05-0.07; 0.04-0.05; 0.03-0.04; 0.02-0.03; 0.01-0.02 and less than 0.01.