Until about the mid-19th century, Sao Paulo was a small trading city and slowly continued to grow in importance through coffee exports (The Slum Challenge , global report on human settlements, 2003, p.226). The city eventually became socially divided between rich and poor, with the rich concentrated in upper central neighborhoods and the poor in flood plains and along railway lines (The Slum Challenge, Global Human Settlements Report, 2003, p 226). To make this socio-spatial segregation even more important, urbanization increased dramatically between 1930 and 1980, when there was an intense process of migration from the countryside. Throughout the 1980s, major industrial deconcentration caused mid-sized Brazilian cities to grow at rates well above those of metropolises. In large metropolises, this has led to lower or even lower rates of population growth in central areas (The challenge of slums global report on human establishments, 2003, p. 227). This transformation from an industrialized city into a better-served metropolis has accentuated economic and social polarization and quickly widened the income gap between the richest and the poorest. Also around this time, there was an increasing growth of slums on the urban periphery (called favelas in Brazil). According to the global report on human settlements The challenge of slums (2003),