1. introduction: A major shift in the map of human habitation

in 2025, the history of the world's cities has been rewritten. the World Urbanization Prospects 2025 report, released by the United Nations Department of Economic and Social Affairs (UN DESA), formalized a fundamental reshuffling of the global urban hierarchy as we know it. after decades of reigning as the "world's largest city," Tokyo, Japan, has been dethroned. The new number one is none other than Jakarta, the capital of Indonesia.

the report is more than just a ranking change; it signals a massive demographic shift that shows the world's center of gravity is shifting from industrialized Northeast Asia and the West to Southeast Asia, South Asia, and Africa. as of 2025, 45% of the world's 8.2 billion people will live in cities, and the number of "megacities" with more than 10 million people has quadrupled from 8 in 1975 to 33 in 2025.

based on the latest data from the United Nations, this report (blog post) takes an in-depth look at how Jakarta became the world's No. 1 city, the statistical secrets behind its rise and the intense life of Jakartans, and the trends in urbanization in 2025, from the depopulation crisis in Seoul and Tokyo to the explosive growth of African cities.

2. the secret behind the rankings: Degree of Urbanization

many of you may be wondering. "Did Jakarta really have that many people?" or "Did Tokyo suddenly shrink?"

the key to this dramatic shift in rankings lies in a new statistical criterion that the UN introduced with this 2025 revision: the "Degree of Urbanization" methodology.

2.1 Measuring 'real cities' beyond administrative boundaries

in the past, the UN's statistics were based on each country's own definition of "city". some countries considered only the administrative area (City Proper) to be a city, while others used the metropolitan area as a benchmark. This often distorted the true size of cities, especially in developing countries, where cities often sprawl uncontrollably outside of administrative boundaries, resulting in underestimates of population.

beginning with the 2025 report, the UN applied a globally uniform set of geospatial data, dividing the world into a 1 km² grid and defining "urban agglomerations" as areas of contiguous population density above a certain level.

2.2 Rediscovering Jakarta: From 12 million to 42 million

applying this criterion completely changed Jakarta's status. if we looked only at the population of the existing administrative district, the Special Region of Jakarta (DKI Jakarta), it was only in the top 30 in the world at around 12 million. but when we lumped the surrounding satellite cities of Bogor, Depok, Tangerang, and Bekasi, as well as the sprawling metropolitan area, the so-called "Jabodetabek " region, together, the populationrose vertically to 41.9 million.

this giant sea of concrete and humanity surpassed Tokyo (around 33-37 million) to become the world's undisputed number one megacity. this reflects cities as "livability zones" - places where real people live, commute, and work, rather than administrative lines.

3. lives and cancers in Jakarta (Jabodetabek), the world's #1 city

what does a city of 42 million people look like? Jakarta's rise to the top is a triumph for Indonesia's economic growth and urbanization, but it's also a site of great survival in the face of overwhelming population pressure.

3.1 Hellraisers and motorcycle troops: an extreme commuting war

the most defining feature of the Jabodetabek area is the massive commuter traffic heading to the center (Jakarta). jakarta is notorious for having one of the worst traffic jams in the world - locals call it "Macet". it's not uncommon to spend three to four hours a day commuting from the satellite city to the city center, and if it rains, the roads turn into giant parking lots.

life is intense for the people here. office workers in Bogor or Bekasi wake up at 4 or 5 in the morning to start the battle to get to work. public transportation infrastructure hasn't kept up with population growth, so many citizens rely on "ojeks," or motorcycle taxis. acrobatically weaving between tightly packed traffic, ojeks are the lifeblood of Jakarta. negotiating fares with Ojek drivers and racing through the fumes is a daily occurrence for Jakartans. in recent years, public transportation has been expanding, including the MRT (subway) and TransJakarta (BRT), but it's still not enough to keep up with the transportation needs of 40 million people.

3.2 Sinking city and capital relocation

overcrowding isn't the biggest threat facing Jakarta: the city is physically sinking. jakarta is one of the fastest sinking cities in the world, with some areas sinking 25 centimeters per year. this is the result of poor water supply penetration and reckless groundwater extraction. add to that rising sea levels due to climate change, and 40% of the city is already below sea level.

in neighborhoods like Muara Baru in North Jakarta, residents live in homes that are lower than the sea, relying on a single massive concrete barrier. major floods in 2007 and 2020 paralyzed entire cities, and these disasters could repeat themselves at any time.

eventually, the Indonesian government decided to move the capital to Nusantara on the island of Borneo. however, the UN and experts believe that relocating the capital will only go so far in relieving Jakarta's population concentration. while administrative functions may have moved, Jakarta's status as an economic and commercial center remains strong, and its population is expected to continue to grow until 2045.

4. the scary chaser: Dhaka, Bangladesh

hot on Jakarta's heels is Dhaka, the capital of Bangladesh. with a projected population of nearly 40 million in 2025, it ranks second in the world. what's even more surprising is how fast Dhaka is growing. The UN predicts that by 2050, Dhaka will overtake Jakarta to become the world's most populous metropolis.

4.1 A city of climate refugees

dhaka's population explosion is directly linked to "climate change. with much of the country being low-lying, Bangladesh is facing the brunt of sea level rise and cyclones. millions of "climate refugees," displaced from their homes along the southern coast and in rural areas, are flocking to Dhaka in search of shelter. some estimates suggest that around 2,000 new migrants enter Dhaka every day.

4.2 Ultra-high density and slums

this gives Dhaka an unimaginable population density. with a population density of over 20,000 people per square kilometer, huge slums have formed across the city. slums like Korail are built on unstable land alongside lakes and rivers, and are often the first to be submerged during floods. despite this, jobs centered around the garment industry (sewing factories) continue to suck in young labor. dhaka is the frontline of the most dramatic collision between the climate crisis and urbanization facing humanity.

5. northeast Asia at dusk: the Crisis of Tokyo and Seoul

while Jakarta and Dhaka are exploding, Tokyo and Seoul, once the centers of Asia's revival, are facing a severe demographic crisis.

5.1 Tokyo: Past the peak and downhill

after decades at the top of the list, Tokyo has now slipped to third place (33-37 million people). what's worse is the trend. tokyo's population has peaked and begun to decline, and is projected to drop to seventh in the world by 2050. the aging and declining birthrate across Japan is causing even the capital to shrink.

5.2 Seoul: 0.72 impact and concentration in the metropolitan area

seoul, the capital of South Korea, is experiencing a similar - and even more acute - crisis. in the UN report, the Seoul urban area (Sudogwon) is estimated to have a population of around 22.5 to 22.6 million people, ranking it ninth or tenth in the world. this is based on the actual urban area, which includes Incheon and Gyeonggi Province, rather than the administrative area of Seoul (about 9.6 million people).

seoul, however, has a critical problem: it has one of the lowest fertility rates in the world. in 2024, South Korea's total fertility rate is projected to be 0.72 children, less than one-third of the replacement fertility rate (2.1) needed to sustain the population. high housing prices, excessive competition, and difficulty balancing work and family have combined to create a "depopulation" crisis. the UN predicts that by 2050, Seoul will slip out of the world's top 10 most livable cities (12th is expected). this isn't just a drop in ranking, it could mean the loss of a national growth engine.

6. the new frontier: African cities making inroads

while Asian cities are jockeying for position, new megacities are growing at an alarming rate in Africa. The UN has projected that the majority of future urban population growth will occur in Asia and Africa.

6.1 Dar es Salaam: Growth without infrastructure

dar es Salaam, the economic capital of Tanzania, is one of the fastest growing cities in the world. its population growth rate exceeds 5% per year, and it will soon join the 10 million population club (megacities). but its growth is the epitome of "urbanization without infrastructure. roads are chronically congested, water and sewage facilities are woefully inadequate, and nearly half of the city's water supply is lost through leaks or stolen. rapid urbanization has intertwined with poverty, water shortages, and traffic chaos to create a compounding crisis.

6.2 Addis Ababa: construction boom and conflict

addis Ababa, the capital of Ethiopia, is also experiencing incredible growth, averaging over 10% per year. new skyscrapers and light rail are popping up all over the city, but underneath the chaos of old-fashioned Lada taxis and livestock sharing the roads, and the forced displacement and conflict of indigenous people as the city expands.

7. top 10 World Megacities 2025 (according to UN WUP 2025)

here are the world's 10 largest cities in 2025 according to the new criteria (degree of urbanization). (Rankings and figures may vary slightly depending on the specifics of the report.)

rankingcity (Country)population (approx.)characteristics 1 jakarta (Indonesia) 41.9 million people ranked#1 in the world, metropolitan area (Jabodetabek) combined 2 dhaka (Bangladesh) 40 million people climate migration, ultra-high density, projected to be #1 by 2050 3 tokyo (Japan) 33 million people entering population decline, losing top spot 4 delhi (India) 30.2 million people continued rural population influx 5 shanghai (China) 29.6 million people china's largest economic city 6 guangzhou (China) 27.6 million people center of the Pearl River Delta megaregion 7 cairo (Egypt) 23.1 million people The only non-Asian in the top 10 8 manila (Philippines) 24.7 million people high population density and service industry focus 9 kolkata (India) 22.6 million people slow growth rate 10 seoul (South Korea) 22.5 million people includes the metropolitan area, with the world's lowest fertility rate, facing decline

8. closing thoughts: the age of the Global South

the UN World Urbanization Prospects 2025 report sends us a clear message. the era of developed world-style urbanization led by London, New York, and Tokyo is over, and megacities in the "Global South" like Jakarta, Dhaka, Lagos, and Kinshasa have emerged as the future home of humanity.

these new megacities face different challenges than cities of the past. they face poverty as population growth outpaces industrialization, flooding and disaster risks from climate change, and the challenge of supporting tens of millions of people with inadequate infrastructure.

jakarta's rise to the top of the list is not just a numbers game; it's a new self-portrait of the 21st century, shaped by a combination of the climate crisis, the rise of the developing world, and shifting demographics. How we as a species will live sustainably in these sprawling, chaotic, and vibrant cities in the future may be answered by today's Jakarta and Dhaka.