Generally urbanisation is understood as ashift from a predominantly rural to a predominantly urban society. Rapid urbanisation is arguably the most complex and important environmental and socio-economic phenomenon of the 20th and 21st centuries, and is likely to remain a challenge into the 22 century. It represents major and irreversible changes in production and consumption and the way people interact with nature. It is therefore somehow surprising that, within the international debate, it is only recently that cities and the urbanisation process started to be looked at through a ‘sustainability’ lens. The notion that cities play a key role in ‘sustainable development’ only started to become popularised and mainstreamed into policy making and planning since the early 1990s. It is now widely acknowledged that the impact of urbanisation will continue to bring about major global and local changes well into the current century, as many countries in the developing world are presently in, or about to enter, the high-growth and rapid-transition phase of the urbanisation process. The UN predicts that two-thirds of the world's population will live in cities by 2050, this poses a unique infrastructural, environmental, socio-economic challenges for African and Asian countries, where 90% of the growth is predicted to take place.

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Future development targets should focus on creating inclusive cities with adequate infrastructure and services for all residents, said John Wilmoth, director of the UN's population division. "Managing urban areas has become one of the most important development challenges of the 21st century," he said. "Our success or failure in building sustainable cities will be a major factor in the success of the post-2015 UN development agenda." The UN report says rapid urbanisation will bring opportunities for governments to improve access to important services. "Providing public transportation, as well as housing, electricity, water and sanitation for a densely settled population is typically cheaper and less environmentally damaging than providing a similar level of services to a predominantly rural household," it says. While most Europe, America and Arab region are highly urbanized already (over 70%) ,Africa is projected to experience a 16% rise in its urban population by 2050 – making it the most rapidly urbanising region on the planet – as the number of people living in its cities soars to 56%.

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Decisions about health, fertility, migration, productivity,infrastructure, education,governance, natural resources use and so on are increasingly affected by the diffusion power of the urbanization process, not just spatially but through the global economy,informational spill-overs and social networks.

Its becoming increasingly clear that most urban development models setting the urban development agenda for Africa and other places are based on what has worked in the now "global cities" of the developed countries, due to cultural differences and uniquenesses, this could be a source of impediments facing urban development and sustainability in Africa and other places. The conceptualization, analysis and interpretation of sustainable city or urban development  should always take place within the unique context of its historical, geographical, cultural and developmental setting.  This paradigm shift holds the key to sustainable cities or sustainable urban development in Africa and many parts of the wo.

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The UN projects that rural populations will increase in only a third of countries between 2014 and 2050, as states with large rural communities will take longer to urbanize. "In general, the pace of urbanization tends to slow down as a population becomes more urbanized," the report says.

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Is focusing on urban development and completely neglecting the rural a solution or part of the problem? It is becoming clearer that promoting rural development is beneficial to sustainable urbanization: developing rural infrastructure and linking rural and urban, provision of basic services in the rural areas (roads, water, electricity, health, education) is a way of ensuring inclusive human development towards achieving inclusive, sustainable urbanization by 2050 and beyond. The key to inclusive and sustainable urban development lies within striking a balance between the rate of urbanization, rate of urban development and the rate at which the rural population declines vis a vis the rate of rural development.