The growth of Santiago has undergone several changes over the course of its history. In its early years, the city had a rate of growth 2.9% annually until the 17th century, then down to less than 2% per year until the early 20th century figures. During the 20th century, Santiago experienced a demographic explosion as it absorbed migration from mining camps in northern Chile during the economic crisis of the 1930s. The population surged again via migration from rural sectors between 1940 and 1960. This migration was coupled with high fertility rates, and annual growth reached 4.9% between 1952 and 1960. Growth has declined, reaching 1.4% in the early 2000s. The size of the city expanded constantly; The 20,000 hectares Santiago covered in 1960 doubled by 1980, reaching 64,140 hectares in 2002. The population density in Santiago is 8,464 inhabitants/km2.