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However, while megacities might be economic powerhouses, they do not represent the majority of the urban population (see Figure 2.8), and are not the fastest-growing urban centres (see Figure 2.9). Small and medium cities now account for roughly 50 per cent of the world’s urban population and are growing at the fastest rates (UN DESA 2014; United Nations Economic and Social Commission for Asia and the Pacific [UNESCAP] and UN-Habitat 2015). They will “deliver nearly 40 per cent of global growth by 2025, more than the entire developed world and emerging market megacities combined” (UN-Habitat 2015a, p. 2; Dobbs et al. 2011). Small and medium cities are also
Figure 2.8: Global urban population growth propelled by cities 6 000
5 000 4 000 2 3 000 2 000 1 000 0
21 cities 10 cities
294 cities 239 cities
43 cities 417 cities 525 cities
731 cities 558 cities
63 cities 41 cities
more vulnerable to natural hazards than big cities and megacities (Birkmann et al. 2016).
2.4.2 Urban agglomeration economies
Agglomeration economies reflect the advantage of people clustering to reduce transport costs for goods, people and ideas. Higher productivity attracts inflows of people, who in turn further increase productivity. Agglomeration economies thus generate a positive feedback loop and multiply the impact of external productivity factors, and so boost urban populations and wages (Glaeser and Gottlieb 2009; Zenghelis 2017).
Megacities of 10 million or more Cities of 500 000 to 1 million
Source: United Nations (2014, p. 13) Figure 2.9: City growth rates very high high medium low very low 0 mega cities Source: Birkmann et al. (2016) 32 Setting the Stage 1 big cities 2 medium cities 3 small cities 4 Annual average urban population growth rate (%) 5 6
Large cities of 5 to 10 million Urban areas smaller than 500 000