The process of planetary urbanization challenges us to look beyond inherited cartographies and distinctions to understand a worldwide process of urbanization.

" … the urban can no longer be understood with reference to a particular "type" of settlement space, whether defined as a city, a city-region, a metropolis, a metropolitan region, a megalopolis, an edge city or otherwise … Today, the urban represents an increasingly worldwide condition in which political-economic relations are enmeshed. The situation of planetary urbanization means, paradoxically, that even spaces that lie well beyond the traditional city cores and suburban peripheries - from transoceanic shipping lanes, transcontinental highway and railway networks, and worldwide communication infrastructure to alpine and costal tourist enclaves, 'nature' parks, offshore financial centers, agroindustrial catchment zones and erstwhile 'natural' spaces, such as the world's oceans, deserts, jungles, mountain ranges, tundra and atmosphere - have become integral parts of the worldwide urban fabric." - Neil Brenner

In 1903, Simmel wrote an essay, The Metropolis and Mental Life, to understand the psychology of the contemporary city. In the essay, Simmel acknowledges that cities increase the day-to-day stimuli that city dwellers face in their everyday lives. Compared to people in small towns, they come into contact with hundreds - maybe thousands - of people each day, most of whom are strangers.

"Thus, the metropolitan type - which naturally takes on a thousand different modifications - creates a protective organ for itself against the profound disruptions with which the fluctuations and discontinuities of the external milieu threaten it. Instead or reacting emotionally, the metropolitan type reacts primarily in a rational manner, thus creating a mental predominance through the intensification of consciousness, which in turn is caused by it."

Simmel suggests that the only way to survive everyday life in the contemporary city is through the adoption of a blasé attitude.

"If the unceasing external contact of numbers of persons in the city should be met by the same number of inner reactions as in the small town, in which one knows almost every person he meets and to each of whom he has a positive relationship, one would be completely atomized internally and would fall into an unthinkable mental condition."

The Swiss architect, LeCorbusier, laid out his plans for the Radiant City in a book, The City of Tomorrow and Its Planning.

LeCorbusier was reacting to the cities of his era, and particularly, to the winding mess of crooked streets in Paris. He expressed contempt for the unplanned, disorganized chaos of the modern city.

“Paris provided both (LeCorbusier’s) raw material and his vision of an ideal order. Just as Howard cannot be understood save in the context of late nineteenth-century London, or Mumford save in that of the New York of the 1920s, so all Corbusier’s ideas need to be seen as a reaction to the city in which he lived and worked from 1916 until shortly before his death in 1965. The history of Paris has been one of constant struggle between the forces of exuberant, chaotic, often sordid everyday life and the forces of centralized, despotic order. In the 1920s and the 1930s, it was clear that chaos was winning and order had been in long retreat.” - Robert Fishman

Against the crooked, winding streets of the European cities, LeCorbusier argued for straight lines and right-angles as the centerpiece of the organized metropolis. These angled streets served a social purpose, as well as a physical one, underscoring the importance of utopian planning as a social project.

"Paris is a dangerous magma of human beings gathered from every quarter by conquest, growth and immigration; she is the eternal gypsy encampment from all the world's great roads; Paris is the seat of power and the home of a spirit which could enlighten the world; she digs and hacks through her undergrowth, and out of these evils she is tending toward an ordered system of straight lines and right angles; this reorganization is necessary to her vitality, health and permanence; this clearing process is indispensable to the expression of her spirit." - Le Corbusier

City planning, according to LeCorbusier, was too important to be left in the hands of everyday people. Instead, he argued for the expertise of the city planner and the science of a profession to design cities.

LeCorbusier planned to decongest the center of the city by creating organized density at the heart of his cities. Towers in the park would increase the verticality of cities and create open parks and green spaces. In LeCorbusier's city, the skyscraper would be build to a density of 1,200 people to the acre, and the residential blocks would be 120 to the acre. These are substantially more dense than other cities, including London and Paris

Radiant City would facilitate and rationalize plans for mobility in the city, including multiple levels of roadway for automobile traffic. It would separate slow-moving traffic from fast-moving traffic, and include below-ground roads for heavy traffic and ground-level roads for ordinary traffic. Pedestrian traffic would be separated from car traffic.

"But a modern city lives by the straight line, inevitably; for the construction of buildings, sewers and tunnels, highways, pavement. The circulation of traffic demands the straight line; it is the proper thing for the heart of the city. The curve is ruinous, difficult and dangerous; it is a paralyzing thing."

One of the fiercest critics of utopian planning - and of LeCorbusier and his acolytes, in particular - was the urbanist, Jane Jacobs. In her 1961 book, Death and Life of Great American Cities, Jacobs critiques the "Radiant-Garden-City Beautiful".

Jacobs argued that utopian planners neglected to see the on-the-ground social relations that made city neighborhoods lively, vibrant places. Although their schemes were never built in their entirety, their ideas trickled into the plans for cities throughout the twentieth century.

"LeCorbusier's dream city has had an immense impact on our cities. It was hailed deliriously by architects, and has gradually been embodied in scores of projects, ranging from low-income public housing to office building projects ... He attempted to make planning for the automobile an integral part of his scheme, and this was, in the 1920's and early 1930's, a new, exciting idea. He included great arterial roads for express, one-way traffic. He proposed underground streets for heavy vehicles and deliveries, and of course, like the Garden City, he kept pedestrians off the streets and in the parks. His city was like a wonderful mechanical toy." - Jane Jacobs

The work of utopian planners was as much a social or political construct as it was a physical plan for a city. Jacobs noted that LeCorbusier attempted to plan away the joys of unplanned encounters that were so important to vibrant, lively cities.

"LeCorbusier was planning not only a physical environment. He was planning for a social utopia, too. LeCorbusier's Utopia was a condition of what he called maximum individual liberty, by which he seems to have meant not liberty to do anything much, but liberty from ordinary responsibility. In his Radiant City, nobody, presumably, was ever going to have to be his brother's keeper anymore. Nobody was going to have to struggle with plans of his own. Nobody was going to be tied down." - Jane Jacobs

According to Jacobs, plans for utopian cities ignored the unexpected, inventive aspects that made cities wondrous human creations.

" ... he simply wrote off the intricate, many-faceted, cultural life of the metropolis. He was uninterested in such problems as the way great cities police themselves, or exchange ideas, or operate politically, or invent new economic arrangements, and he was oblivious to devising ways to strengthen these functions because, after all, he was not designing for this kind of life in any case."

The period of widespread, post-War suburbanization in the United States created new socio-spatial forms. Although we tend to consider suburbanization as a reflection of citizens' preferences, this process was deeply facilitated by federal efforts to expand homeownership and create new types of residential locations.

First, the growth of the suburbs forced analysts of urban life to consider the city in relation to the surrounding suburb. Along with these suburbs, we eventually saw the growth of Edge Cities, ex-urbs, and metropolitan regions, challenging us to look at the ecosystem of the city to understand contemporary urban life.

Second, with white flight from the city, Americans left behind cities that were deeply segregated. The concentration of African-Americans in urban neighborhoods generated a legacy of racial segregation and exclusion that persists today.

Finally, these patterns of migration resulted in the ghettoization of poor, African-American families in neighborhoods of concentrated disadvantage. Sociologists use the terminology of "neighborhood effects" to understand why - and how - neighborhoods of concentrated disadvantage shape the lives of the urban poor.

In 1991, sociologist Saskia Sassen published a book, The Global City, detailing the growing importance of cities in an era of globalization. Responding to concerns that place generally - and cities, in particular - were becoming less relevant in an era of growing interconnectedness, Sassen argued that cities were, in fact, more important than ever.

“Rather than becoming obsolete because of global geographic dispersal and integration made possible by information technologies, cities became strategic.”

Specifically, Sassen argued that a handful of cities were critical as the command and control centers of the global economy. The global economy relied on these cities to function effectively.

“Global cities are strategic sites for the management of the global economy and the production of the most advanced services and financial operations that have become key inputs for that work of managing global economic operations.”

From the discussion of global cities, other urban theorists have argued that we should instead be concerned not about a handful of cities, but about the degree of integration (of all cities) into the global economy. We can evaluate this integration, including the flow of migrants, information and capital, for cities around the world.

Yet, this process of globalization has also created new forms of social inequalities concentrated in urban areas. Specifically, the rise of a high-end labor market and a low-wage labor market has hastened the creation of a 'dual city' of entrenched inequality.

“Developments in cities cannot be understood in isolation from fundamental changes in the larger organization of advanced economies … The group of service industries that were one of the driving economic forces beginning in the 1980s and continue as such today is characterized by greater earnings and occupational dispersion, weak unions, and a growing share of casualized low-wage jobs along with a growing share of high-income jobs.” - Saskia Sassen

Globalization introduced questions about the rescaling away from the nation-state as an actor and toward cities as key actors.

The twenty-first century study of cities would be incomplete without an analysis of the G-word: Gentrification. While occasionally described as urban renewal, redevelopment or an urban renaissance, gentrification generally refers to the productive reinvestment of capital in once-neglected urban neighborhoods and the return of high-socioeconomic status residents to disadvantaged neighborhoods.

First, gentrification raises questions about authenticity. In her book, Naked City: The Death and Life of Authentic Urban Spaces, Zukin introduces debates over what makes for an authentic urban neighborhood.

Second, gentrification often involves the repurposing of the built infrastructure of the city. What do we do with the old factories of SoHo or the decaying public housing developments of Red Hook, for example?

Finally, gentrification forces us to ask about the right to the city. Who has a right to shape, occupy and transform urban neighborhoods? Do property rights trump all other rights, or can rights to the city derive from simply living in a neighborhood and participating as a community actor?

“We are, all of us, architects, of a sort. We individually and collectively make the city through our daily actions and our political, intellectual and economic engagements. But, in return, the city makes us.” - David Harvey

Lagos, Nigeria: The Rise of the Mega-City

• Megacities are cities with more than 10 million inhabitants. By comparison, the population of some major American cities: Chicago has 2.7 million people, Denver has 640,000 people, Washington, DC has 660,000 people and Houston has 2.2 million people.
• In 1990, there were 10 megacities and they were home to about 153 million people. Today, there are 28 megacities and they are home to 453 million people. By 2030, there will be 41 megacities, concentrated largely in India, China and other parts of Asia.

By 2050, demographers expect Lagos, Nigeria to double in size, growing into one of the largest cities in the world.

One of the core challenges to this megacity growth is to promote urbanization that is environmentally sustainable. Although cities are often more sustainable, especially as density can decrease energy use and encourage public transportation, the growth of megacities can raise concerns about the prospects of urban sustainability.

In addition to concerns about sustainability, mega-cities introduce challenges to building infrastructure, consuming natural resources, creating structures of democracy, and ensuring opportunities for workers in the informal sector.

Dadaab, Kenya: The Rise of the Unplanned City

Human Rights Watch researcher, Ben Rawlence, explores the tremendous growth of Dadaab, a refugee camp in northern Kenya, in his book, City of Thorns: Nine Lives in the World's Largest Refugee Camp.

The camp emerged as a response to the global political crisis in nearby Somalia. Its population has grown six-hold in twenty-five years - a remarkable growth by any stretch.

"The term 'refugee camp' is misleading. Dadaab was established in 1992 to hold 90,000 refugees fleeing Somalia's civil war. At the beginning of 2016, it is twenty-five years old and nearly half a million strong, an urban area the size of New Orleans, Bristol or Zurich unmarked on any official map."

In City of Thorns, Rawlence describes a camp as having many of the attributes of a modern city - patterns of spatial segregation, a robust series of markets, external forces shaping the growth and development of the camp, (semi-) permanent housing and buildings, etc. Unplanned cities, like Dadaab, present another set of urban challenges associated with housing populations fleeing civil wars, caught in the middle of political violence, or uprooted from their homes through other global processes, including environmental destruction.

Zhengzhou, China: The Rise of the Ghost City

Planning for an unprecedented movement to cities in the next couple decades, China has seen a rise of "ghost cities" - places with the built infrastructure of cities ... but no people.

"Throughout China, there are hundreds of cities that have almost everything one needs for a modern, urban lifestyle: high-rise apartment complexes, developed waterfronts, skyscrapers, and even public art. Everything, that is, except one: people. These mysterious - and almost completely empty - cities are a part of China's larger plan to move 250 million citizens currently living in rural areas into urban locations ..." - Sarah Jacobs, Business Insider

Over the next couple decades, demographers expect the urban population in China to exceed one billion people - an increase of 250 million people.

Dubai, United Arab Emirates: The Rise of a Glistening City

And yet, in contrast to the hundreds of 'ghost cities' on the inland of China, we are also seeing the rise of a new type of high-rise, high-priced city in places like Abu Dhabi, Dubai and Shanghai (Pudong). In many ways, these are cities of tomorrow. Their fantastic architecture seems almost futuristic.

In Dubai, the discovery of oil in the 1960s started the major infrastructure developments that would, over the next fifty years, lead to the emergence of a world-class city. By the 1980s, leaders of the UAE had decided to make Dubai into a city for international tourism - world-class hotels, sporting events, entertainment and architecture would officially put Dubai on the map. In their quest to become a 'world city', cities like Dubai compete for high-income tourists and capital as part of a vast, interconnected network of places.

Detroit, Michigan: A Shrinking City

When Detroit declared bankruptcy in 2013, it was the largest American municipality to have done so. Following decades of population growth in the early-twentieth century, Detroit, like many other cities, experienced an incredible population decline over the second half of the twentieth century.

From a city of nearly 2 million people in the post-War period, Detroit is now a city of less than 700,000 people. Unlike cities experiencing rapid population growth, Detroit is trying to figure out how to manage a smaller - and shrinking - city.

"The hope is that Detroit Future City will inspire decision-makers at all levels — block club presidents and city councilmembers, community patrol leaders and investors — to make choices that align with a coherent vision for a city that is working to become whole after decades of bleeding."

The challenges of a shrinking population include offering high-quality services in shrinking neighborhoods, revitalizing communities without displacing existing populations, and ensuring that the city remains economically viable in a post-industrial era.

Syracuse, New York: A City Divided by a Highway

In Syracuse, the construction of Interstate-81 sliced straight through the heart of downtown in the 1960s during a period of Urban Renewal. As in many cities, the result was a series of neighborhoods largely cut-off from the fabric of the city.

Los Angeles: Retrofitting a City of Sprawl

One of the legacies of post-War suburbanization was the creation of urban sprawl in metropolitan areas throughout the country. Sprawl poses unique challenges to the built infrastructure of cities as car-centered developments create stark environmental and health challenges.

Dharavi, Mumbai, India: Slums in a Globalizing City

Located in the heart of globalizing Mumbai, the slums of Dharavi now sit atop a valuable square mile of land. Slums are characterized by a lack of basic services, substandard housing conditions, density and overcrowding, insecure residential tenure, and marginalization from the broader urban fabric. Dharavi houses between 300,000 and 1 million people in a single square mile - about the size of the Georgetown neighborhood.

According to UN-Habitat, 180,000 people are moving to slums every day in cities of the Global South. Mike Davis, the author of Planet of Slums, notes that the slum population in cities around the world will grow faster than the rest of the urban population. By 2050, as many as 2 billion people - fully one-third of the global urban population - is expected to live in a slum.

“Urban segregation is not a frozen status quo, but rather a ceaseless social war in which the state intervenes regularly in the name of ‘progress,’ ‘beautification,’ and even ‘social justice for the poor’ to redraw spatial boundaries to the advantage of landowners, foreign investors, elite homeowners, and middle-class commuters.” - Mike Davis

As real estate values skyrocket in Mumbai, planners in the city need to figure out ways to balance competing claims to the city. The slums of Dharavi raise important twenty-first century questions about land tenure, neoliberal urban strategies, and negotiations of the competing rights to the city.

East of the River, or River East: The Costs and Benefits of Gentrification

“Gentrification” has become the accepted term to describe neighborhoods that start off predominantly occupied by households of relatively low socioeconomic status, and then experience an inflow of higher socioeconomic status households ... Since entering the mainstream lexicon, the word “gentrification” is applied broadly and interchangeably to describe a range of neighborhood changes, including rising incomes, changing racial composition, shifting commercial activity, and displacement of original residents." - Furman Center for Real Estate and Urban Policy

Gentrification encourages us to ask about the ways that state actors (e.g., local governments) promote development and the role of private capital in reshaping cities. We need to confront questions about how neighborhoods got to be 'gentrifiable,' and what can be done to share the benefits of neighborhood change more evenly.