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44 Managing Systems of Secondary CitiesTable 3.4Number of Cities by Population Size 1995, 2010, 2025 (estimated)>10 million 5-10 million 1-5 million 0.5-1 millionWorldAfricaSub-Saharan AfricaAsiaEuropeLatin America/CaribbeanNorthern AmericaOceania199513––7–42201023211324220253732223631995192111321–2010381125345–20255997323591199527026211194737365201038847401884955436202557281713055774505199533836291397751341201051355442748360392202575091714249673606Source: UN Urban Prospectus (2011)Asia is expected to experience the most significant increase in the growth and developmentof secondary cities. More than 60 per cent of the increase in the number of cities(population range 05-0.5 million) will occur in Asia. However, in Africa, particularlysub-Saharan Africa, growth pressures will fall proportionally in the development ofsecondary cities in the 0.5-1 and 1-5 million city sizes. An additional 27 cities of 1-5million and 31 of 0.5-1 million people are expected to develop in sub-Saharan Africaby 2025. Figure 3.1 shows the expected number of cities by size by region 2010-2025.3.3 Geographic Primacy and Dispersion of CitiesThe geographic primacy and dispersion of cities vary significantly between countriesand regions. Table 3.5 shows the proportion of cities, by type, with populations ofmore than 500,000 for different regions and subregions of the world. Regions wherethe proportion of smaller-sized cities (0.5-5 million) is higher than the global averagetend to have a more dispersed (D) geography of cities. Regions where this is lowertend to have higher levels of primacy (P). Although the assessment approach used isgeneral, it does provide a useful indicator of the dominance of a small number of largecities on the urban economic geography of regions. Factors such as climate, resourceabundance and political economy can have a significant effect on shaping the economicgeography of cities. However, the level of primacy and dispersion of cities will have asignificant impact on how governments formulate policies and programmes for urbanand regional economic development.There are significant regional differences in the geographic patterns of systems ofcities. In Asia it is generally dispersed, with countries such as India and China having