What is a megacity?
A megacity is usually defined as a metropolitan area with a total population in excess of 10 million people. Some definitions also set a minimum population density (such as 2,000 persons per square km) or define a megacity as a metropolitan area with more than 20 million people.
According to the United Nations, a megacity can be defined as “a very large city, typically with a population of over 10 million people”. The term “megacity” entered common use in the late 19th or early 20th centuries; back then New York and London were the only cities that could be defined as megacities.
In 2023, there are about 35 megacities worldwide, with Tokyo being the largest at around 37 million inhabitants. Other examples of current megacities include Delhi, Shanghai, Sao Paulo, Mexico City and Cairo. The number of megacities is projected to rise to 43 by 2030.
So in summary, the standard definition is that a city needs a total metropolitan area population of over 10 million to be considered a megacity. The strict population threshold is 10 million, but some may argue that an area with 8-9 million could also potentially qualify.
A brief history of megacities
The emergence of megacities is a relatively new phenomenon in human history. For most of history, the world’s largest cities tended to have populations numbering in the low hundreds of thousands. It was only after the Industrial Revolution in the 1800s that cities started to dramatically expand in population.
London became the first city to reach 1 million inhabitants around 1810. New York hit the 1 million mark not long after in the 1870s. These were the first cities in history to gain “megacity” status by modern definitions.
A few decades later, Tokyo joined the club as the first megacity outside Europe or America with over 1 million people in 1900. By 1920, New York and London both had expanded to around 7 million inhabitants.
After World War II, there was rapid urbanization around the globe and new megacities started emerging, especially in the developing world. Tokyo reached 10 million by 1960. Mexico City, Sao Paulo and Shanghai gained megacity status by the 1970s and 1980s as industrialization took hold in their countries
The trend accelerated in the 1990s and 2000s with the rise of globalization. Dozens of new megacities emerged, mostly in Asia, Latin America and Africa. Many experts believe the number and size of megacities will continue increasing over the next few decades, particularly in the developing world.
So in just over 100 years, the idea of cities with 10 million+ inhabitants went from virtually unthinkable to relatively commonplace around the world. The minimum population to be a megacity has remained quite stable at 10 million since the term was coined, even as the largest cities have continued to rapidly expand in size.
Current megacities of the world
Here is an overview of the largest megacities in 2023, according to population estimates published by the United Nations:
| Rank | City | Country | Population |
| 1 | Tokyo | Japan | 37 million |
| 2 | Delhi | India | 29 million |
| 3 | Shanghai | China | 26 million |
| 4 | São Paulo | Brazil | 22 million |
| 5 | Mexico City | Mexico | 21 million |
| 6 | Cairo | Egypt | 20 million |
| 7 | Mumbai | India | 20 million |
| 8 | Beijing | China | 19 million |
| 9 | Dhaka | Bangladesh | 19 million |
| 10 | Osaka | Japan | 18 million |
Tokyo remains the world’s largest megacity by a significant margin, with around 37 million residents in its metropolitan area despite Japan’s overall population decline. The Tokyo metro area has held the top megacity spot for over 60 years now.
Asia dominates the current megacity rankings, holding 7 of the top 10 spots. But major megacities also exist in Latin America, Africa and Europe.
As can be seen, a population of at least 10 million is needed to be considered a megacity by modern standards. The majority of megacities have total metro populations between 10-20 million. Only Tokyo and Delhi currently exceed 25 million residents.
Projected future megacities
According to projections from groups like the UN, the number and size of megacities will continue to expand over the next few decades:
– The UN estimates there will be 41 megacities worldwide by 2035, up from 35 today. So about 6 more cities will gain megacity status in the next 10-15 years.
– Other organizations like McKinsey Consulting have estimated there could be over 50 megacities by 2025 and more than 70 by 2040.
– Nearly all of this projected megacity growth is expected to occur in developing countries in regions like Asia, Africa and Latin America. For example, Lagos, Nigeria is projected to join the megacity club by 2030.
– Several current megacities like Tokyo, Mumbai and Dhaka are forecast to grow to over 30 million residents by 2030.
– By 2040, the UN projects that Tokyo, Delhi and Shanghai could all reach populations of over 40 million, making them “gargantuan cities” dwarfing anything seen before.
So in the future, the bar for becoming a megacity may remain 10 million, but the world’s largest cities are expected to become even more mega in scale. Vast urban areas of 20, 30, 40 million or more people could become commonplace, especially in the developing world. This will create major challenges for infrastructure, transportation, housing, resources and governance in these future megacities.
Factors driving megacity growth
There are a few key factors that have contributed to the rapid growth of megacities over the last century:
– Global urbanization – More people worldwide are moving to urban areas. The UN estimates that close to 70% of the world’s population will live in cities by 2050, up from 30% in the 1950s. This is driving overall population growth in major metropolitan areas.
– Rural-urban migration – In many developing countries, people are leaving rural farmland to seek economic opportunities in large cities, driving urban expansion. Cities offer more manufacturing, services, education and technology sector jobs.
– Industrialization – Modern manufacturing and industry tends to cluster in and around large cities. This results in more jobs and higher incomes, attracting migrants.
– Technology/globalization – Advances in areas like transportation and communications have enabled megacities to manage large populations and higher densities. Globalized trade networks make it advantageous for firms to locate in major hubs.
– Government policies – Some national policies encourage urbanization by investing in city infrastructure vs rural areas or moving government operations to major cities.
– Natural increase – Megacities often have high birth rates/young populations due to rural migrants, driving population growth from natural increase even if migration stopped.
So in general, urbanization and economic forces lead more and more people to move to and remain in the largest cities every year. This self-reinforcing cycle is likely to continue in many parts of the world, resulting in more megacities in the future.
Challenges posed by megacities
While megacities can stimulate economic growth, innovation and opportunities, they also pose many challenges for governments due to their massive scale:
– Infrastructure – Transport, power, water and telecoms systems must expand to meet needs of tens of millions of residents. Traffic congestion and crowding are common problems.
– Housing – Accommodating millions of new city migrants requires huge amounts of affordable housing units. Slums and homelessness often increase.
– Pollution – Concentrated populations and industries produce massive volumes of air/water pollution, garbage and carbon emissions.
– Resources – Securing adequate food, water and energy to supply megacities requires extensive regional/national networks.
– Income inequality – Wealth gaps between rich and poor urban residents often grow larger in megacities. Lack of services in slums raises social tensions.
– Disease – Crowded megacities can become hotspots for the spread of infectious diseases. Public health systems are stretched.
– Crime – Anonymity, poverty and lack of law enforcement can cause higher crime/violence rates in some megacities vs national averages.
– Governance – Managing a city of 10+ million diverse residents presents administrative challenges with budgets, regulations and planning.
In addition, any man-made or natural disaster or disruption risks causing chaos in a densely packed megacity. Climate change will further strain resources and infrastructure in many major coastal cities going forward.
Megacity governments need forward-thinking policies and leadership to try to address these challenges in sustainable and equitable ways as their populations continue growing.
Advantages of megacities
Despite the challenges outlined above, megacities also create many advantages when managed properly:
– Economic output – Megacities produce a disproportionate share of national GDP. Tokyo accounts for over a third of Japan’s total economic output, for instance. Dense urban areas increase productivity.
– Innovation – The concentration of companies, universities, researchers and institutions in megacities fosters innovation and technological advancement.
– Culture – Large urban centers are hubs for media, arts, entertainment that enrich cultural life for residents.
– Diversity – Megacities tend to be ethnically/culturally diverse, exposing residents to broader experiences.
– Mobility – People in megacities have greater access to economic and social mobility and opportunity compared to rural populations.
– Infrastructure – Heavy upfront investment in “fixed capital” like metro systems and utilities can benefit residents for generations.
– Services – Economies of scale enable cost-effective delivery of utilities, healthcare, education and social services to millions of citizens.
– Sustainability – Compact megacities generally have smaller environmental/energy footprints per capita than dispersed cities and suburbs.
– Knowledge networks – Hyperconnected, high-skill workforces concentrate in megacities, enabling collaboration and innovation.
In summary, megacities act as economic engines and offer expanded opportunities for their residents – if their scale and growth can be properly managed by policymakers. Striking an optimal balance is key.
Urbanization and development trends
The rise of megacities is closely tied to a nation’s overall development level:
– In early stages of development, people move from rural areas to mid-size cities for basic manufacturing jobs. These small/medium urban centers grow in population first.
– As a country becomes more industrialized, these manufacturing centers evolve into major metro areas with over 1 million people through continued migration and increasing productivity.
– Eventually a select few urban centers with advantage geographical locations, concentrations of higher-end services and long-term fixed capital investments emerge as megacities with over 10 million residents.
But this sequence has changed in recent decades. Globalization means some developing countries are now rapidly building megacities from scratch without passing through gradual urbanization first. Countries want modern megacities to compete in the global economy.
For example, China consciously created hundreds of new cities and transformed Shanghai into a megacity over just a few decades. Other countries like Nigeria and India see runaway megacity growth from rural migrants, bypassing medium-sized cities and straining underdeveloped infrastructure.
So the path to megacities is accelerating for today’s developing nations compared to the centuries-long evolution in Europe and North America. This can create unique sustainability issues modern-era megacities must contend with.
Definitions of megacity vary by region
While 10 million residents is the general consensus for a megacity definition worldwide, some countries and organizations use lower population thresholds to define the term locally:
– In India, urban areas with over 4 million people are considered megacities. By this standard, India has dozens of megacities.
– 5 million is used as a megacity benchmark in some academic studies focused on sub-Saharan Africa or South Asia. Lagos and Kinshasa would qualify.
– Experts say the living conditions of an average slum resident in Mumbai with 20 million people may resemble those in a mid-size 1 million city elsewhere. So quality of life metrics matter.
– Relative to national populations, urban centers over 5-7% of the country’s population could be viewed as equivalent to a 10 million megacity.
– Future population projections are also a factor. Cities expected to surpass 10 million imminently are sometimes included in megacity analysis.
So while 10 million remains the common baseline, the practical concept of a megacity may be considered more flexibly in different geographical contexts. Cities do not cross a magic threshold the moment they hit 10 million residents.
Largest cities through history
For historical context, here are the largest cities in the world by population through different eras, based on historical estimates:
| Year | Largest city | Population |
| 150 AD | Rome | Over 1 million |
| 13th century | Hangzhou | Over 1 million |
| 1600 | Beijing | Over 1 million |
| 1700 | Beijing | Over 1.5 million |
| 1800 | Beijing | Over 1.5 million |
| 1900 | London | 6.5 million |
| 1950 | New York | 12.3 million |
| 2000 | Tokyo | 26.4 million |
Until the 19th century, most of the largest cities in the world had populations under 2 million. Beijing was the leading megacity for centuries with over 1 million residents.
London and then New York emerged as the first modern megacities during the Industrial Revolution, a period of rapid urbanization. But it was only in the 20th century that cities with over 10 million people became common.
No city in history exceeded 13 million until Tokyo did so in the 1960s. Tokyo remains the world’s largest urban area by far, despite some cities having much faster growth rates in recent decades.
Megacity trends in the United States
The United States has several metropolitan areas with over 10 million residents that qualify as megacities:
– The New York metro area (including Northern New Jersey and Long Island) contains around 20 million residents as of 2022, making it second only to Tokyo globally.
– The Los Angeles metro area follows with around 13 million residents.
– The Chicago area has about 9.5 million residents, right on the cusp of megacity status.
Dallas, Houston, Washington DC and others are major US metros with populations between 5-7 million, but fall short of the 10 million megacity benchmark.
Unlike other regions like Asia and Africa that are projected to gain many new megacities, continued relatively slow population growth in already built-up cities means the US is not expected to add any new megacities this century.
US urban planners face challenges adapting aging east coast cities like New York and infrastructure in fast-growing Sun Belt metros like Dallas to 21st century needs. But overall, US cities are not seeing the hypergrowth of developing world megacities.
However, some experts argue that using traditional city limit population understates the true size of US metro regions. Metropolitan statistical areas show how American cities have decentralized into expansive metro regions covering thousands of square miles.
So while the central city population of Los Angeles is only around 4 million, its metropolitan area is around 13 million – a megacity by global standards. American cities have transformed into diffuse “megaregions” rather than concentrated megacities.
Conclusion
In review, a megacity is generally defined as an urban metropolitan area with a total population over 10 million people. This population threshold has stayed remarkably consistent over the last 100 years as ever more cities around the world have reached and exceeded this megacity benchmark, especially in the developing world.
Projections suggest there could be over 50 megacities globally by mid-century. The associated opportunities and challenges for infrastructure, resources, inequality, the environment and governance in these massive cities are immense.
Striking an optimal balance between density and livability as these urban behemoths continue expanding will require foresight and leadership. But if well-managed, megacities can drive innovation, economic growth, and social mobility for millions around the world. They are centers of civilization on an unprecedented scale in human history.