Determinants of urban growth during demographic and mobility transitions: Evidence from India, Mexico, and the US

Understanding how and why urban populations grow over time is fundamental for a variety of scholarly and policy arenas including migration, economic development, and environmental change. Improved understanding would also allow for better projections of the future course of urbanization and its consequences for society and the environment. Indemographic terms, aggregate urban growth at the national level is determined by a combination of natural increase (births minus deaths) within urban areas, migration between rural and urban areas or to/from other countries, and the reclassification of land (and population living on it) from rural to urban. Reclassification typically occurs through the expansion of urban boundaries, resulting in larger contiguous areas of urban settlement, or through the addition of distinct new urban areas as rural areas grow in population and economic size and density, contributing positively tourban growth (UN 2001). In some instances, however, reclassification canaffect urban growth negatively because of contraction of existing urbanboundaries or subtraction of existing urban settlements. Conceptually, re-classification is not entirely distinct from the other determinants of growth, because it typically occurs under conditions of increasing population and economic densities. Therefore both natural population growth and migration may indirectly contribute to reclassification by increasing population density in areas that later are reclassified as urban.