Mega city archetype	Character	Population (size)
Emerging Cities	Characterized by high growth rates driven by migration and natural growth, much of which occurs in informal settlements not served by the installed base of infrastructure and services. Social polarity and the gaps in wealth, health, education, and political power between groups is generally highest in Emerging cities.	Annual growth rates are on the order of between 3% and 6%. A 3.5% growth rate implies a doubling of population in 20 years. This includes countries with urban populations of less than 50%. Populations tend to be younger and more male, with a high proportion of poorly educated rural migrants.
Transitional Cities	Often developed mechanisms to more effectively manage dynamic growth, and may be seeing a slowing of annual growth rates. Transitional cities have similar infrastructure challenges as compared with Emerging cities but are better able to respond financially and organizationally. Increasing affluence in these cities places additional new demands on infrastructure as growth in demand for transportation, water, energy, and services often greatly outpaces population growth.	Continued population growth stems largely from migration, with lower natural population increases Several of these cities are seeing the first signs of an ageing population. Growth rates are typically of the order of 2% - 3% per annum and Transitional cities are often in countries that are more than 50% urbanized.
Mature Cities	Have built out their basic infrastructure to serve their populations one or two generations ago. With high-quality infrastructure in place the challenge has shifted to coping with the need for renewal of ageing systems or to dealing with obsolescence where the installed infrastructure no longer meets regulatory requirements.	Mature megacities have much slower growth rates than both Emerging and Transitional megacities, at around 1% on average. In some of these cities, the population has stagnated or is shrinking. Mature megacities also have older population profiles. They exist in countries that are typically around 75% urban.