Cities are perhaps one of humanity’s most complex creations, never finished, never definitive. They are like a journey that never ends. Their evolution is determined by their ascent into greatness or their descent into decline. They are the past, the present and the future.
Cities contain both order and chaos. In them reside beauty and ugliness, virtue and vice. They can bring out the best or the worst in humankind. They are the physical manifestation of history and culture and incubators of innovation, industry, technology, entrepreneurship and creativity.
Cities are the materialization of humanity’s noblest ideas, ambitions and aspirations, but when not planned or governed properly, can be the repository of society’s ills. Cities drive national economies by creating wealth, enhancing social development and providing employment but they can also be the breeding grounds for poverty, exclusion and environmental degradation.

Cities and the regions surrounding them have a symbiotic relationship; as long as this relationship is understood and carefully nurtured, both will advance together. Part 1 presents preliminary observations on the spatial identity of the world’s cities, going beyond the “one or two cities tell everything approach” that has dominated urban studies so far. It shows with compelling evidence that the growth of cities is experiencing a dramatic bifurcation: while most cities in the developing world are growing, with some doubling in size every 15 to 30 years, some cities are actually experiencing population loss.
These changes are neither random nor organic; urban growth and decline are a result of a combination of factors, including geographical location, natural population growth, infrastructure development, national policies, corporate strategies and globalization. Understanding the determinants of the growth or decline of cities can help planners to support the processes that lead to harmonious urban development and to deal with some of the negative consequences of urban growth, such as asymmetrical regional development and ruralurban disparities.

In many cities, wealth and poverty coexist in close proximity: rich, well-serviced neighbourhoods are often located next to dense inner-city or peri-urban slum settlements that lack basic services and adequate shelter. A city cannot claim to be harmonious if some groups concentrate resources and opportunities while others remain impoverished and deprived. Income inequalities and shelter deprivations within cities not only threaten the harmony of cities, but of countries as well, as they create social and political fractures within society that fuel social unrest.
Part 2 presents preliminary findings of a global analysis of income and consumption inequality at the city level. The overall conclusion drawn from the findings is that inequality within cities is high in the developing world, especially in Latin America and sub-Saharan Africa, and in some cities, it is actually rising. Part 2 also looks at levels of shelter deprivation in various cities and concludes that not all slum dwellers suffer from the same degree or magnitude of deprivation and not all slums are homogenous. However, inequalities and levels of deprivation vary widely among regions and countries. These differentiated levels of social inequality and exclusion can adversely affect cities’ and regions’ social and economic development.

Like any other organic system, cities consume, metabolize and transform energy, water and materials into goods and waste. Part 3 presents an analysis of energy consumption at the city and household levels, which clearly shows that consumption patterns vary widely between developed and developing regions and between low- and high-income households. Although cities consume a disproportionate share of the world’s energy, and are responsible for a large share of climate-changing greenhouse gas emissions, Part 3 clearly shows that it is not the level of urbanization in a country or the size of a city that determine the quantity of greenhouse gas emissions per capita; rather, the level of emissions is determined by other factors, such as consumption patterns, lifestyles, income levels, urban form and structure and national and local environmental policies.
Part 3 also presents detailed information on how climate change will impact coastal urban settlements that may be adversely affected by climate change and rising sea levels. Using various examples, this Part also shows how cities present a real opportunity to minimize environmental impacts by improving energy efficiency, minimizing urban sprawl, promoting the use of energy-efficient public transport and improving disaster preparedness.

Cities are not just brick and mortar; they represent the dreams, aspirations and hopes of societies. In a way, each city has its own “personality”, with its strengths and weaknesses, failures and successes. A city’s “soul” is exhibited through its cultural heritage, its traditions and its social fabric. Part 4 argues that the management of a city’s human, social, cultural and intellectual assets is as important for harmonious urbanization as the management of its infrastructure, its social amenities and its public spaces. It reflects new and innovative approaches to urban planning and development that engage citizens more directly and that are inclusive and pro-poor. The approaches call for enlightened political leadership, clear long-term political commitments, progressive sectoral and institutional reforms, and mobilization of domestic resources to scale up actions and sustain harmonious urban development. The approaches must also respond to the following emerging priorities and concerns: i) regional or spatial disparities, ii) urban inequalities; iii) urban environmental risks and burdens, including climate change; and iv) metropolitan expansion or the growth of “city-regions”.