Ranking cities by population require some choices: in particular, do you focus only the legal boundaries of the city, or on a metropolitan area? If it’s a metropolitan area, how do you decide on the city limits? According to the World Urbanization Prospects 2025 report from the United Nations Department of Economic and Social Affairs, the most populous city in the world is Jakarta, Indonesia. Their process involves dividing the area into square kilometers,and estimating population density in each square. Here’s their graphic showing the top 10 cities in the world by population in 2000, 2025, and projected for 2050.
It’s interesting to note that Tokyo, the world’s largest city by population in 2000, has grown in population only modestly since then, and isn’t projected to grow further by 2050. However, Jakarta, Dhaka, Shanghai, Karachi,Cairo, and a few others are taking off. I find it hard, with my 20th-century brain, to imagine what it means to have “city” of more than 50 million people.
What got me thinking about Jakarta was an essay by Nithin Coca: “Jakarta’s Remarkable Urban Transit Transformation” (In Development, April 30, 2026). She begins:
For many years, the first word most foreign visitors learned upon moving to Jakarta was macet, traffic jam. Traffic was so bad that transport experts warned in 2013 that if nothing was done, the city could achieve total gridlock, with every part of the city experiencing a traffic jam. In 2014, Jakarta was crowned the world’s most congested city by the Stop-Start Index and a year later was ranked far below other Asian cities on livability by the Economist Intelligence Unit.
Ten years later, Jakarta has the world’s largest and one of the most used bus rapid transit (BRT) systems. The old, crowded diesel commuter trains, famous for allowing passengers to ride on the roofs, are now electrified, air conditioned, and run on regular schedules linking the suburbs to the city center. There are multiple subway and light rail lines crisscrossing the city. The transformation has been remarkable: in 2015, less than 20% of residents were within walking distance of transit. Now, nearly 90% of the city has access to BRT or trains.
How did this happen? One answer is that traffic and pollution concerns had gotten really bad. “Jakarta had also become one of the world’s most polluted cities. By 2011, 58 percent of all illnesses among people living in the city were related to air pollution. … Residents were resigned to spending an average of 16 days stuck in traffic each year.”
Then a former governor of Jakarta was elected president of Indonesia, and used the position to push for a mass transit system. Indonesia then got a low-interest loan from Japan’s development agency. The deal was: “Japan would play a role in basic design, construction, and introduction of transportation systems, including trains, signals, and gate systems, as well as their operation and maintenance. But Japanese contractors were insistent that, while they might build the railway, it was up to Indonesia to run it. Much of the technology would come from Japanese companies like Sumitomo and Nippon Sharyo, but construction, operations, and maintenance would all have to be done by Indonesian companies or the government.” As the system has been built out, a South Korean consortium has become involved as well.
But the story is only a partial success. Jakarta’s population is growing so fast that what has been built so far is far from adequate. Even with expanded mass transit, the number of cars continues to expand as well. “Danny Djarum, an Air Quality Senior Research Lead at WRI Indonesia says that PM 2.5, the measurement of inhalable airborne particulate matter, is now eight to ten times higher than World Health Organization guidelines. `We’re still one of the top 5 most polluted cities in the world, he said.”
Jakarta’s mass transit system continues to expand. But in addition, one intriguing suggestion is to designate certain parts of the city as “low emissions zones,” where access by private vehicles is restricted, green space is expanded and walkability improved.” Another policy suggestion is some form of congestion pricing.
But overall, Jakarta is showing that if you have a local political determination and are also willing to hire and to heed the world’s top experts to manage the project, a big start toward working mass transit system for the world’s largest city can happen in a decade. “In the latest TomTom traffic index, measuring average congestion—the percentage increase in travel time compared to free-flow conditions— the city ranked 24th, just ahead of the United States’ most famous traffic clogged city, Los Angeles.”
