Greater Mexico City was the fastest growing metropolitan area in the country until the late 1980s. Since then, and through a policy of decentralization in order to reduce the environmental pollutants of the growing conurbation, the annual rate of growth of the agglomeration has decreased, and it is lower than that of the other four largest metropolitan areas (namely Greater Guadalajara, Greater Monterrey, Greater Puebla and Greater Toluca) even though it is still positive.