It's not always as straightforward as it may seem to measure the size of a city or urban region.

There's the problem of which urban boundary to use. And then once you've landed on that, there's the additional problem of estimating how many people live within it. This can be particularly challenging when it comes to informal settlements, where there isn't reliable population data.

The most common approach is to use the continuous built-up area as the urban agglomeration, as opposed to any sort of "city proper" boundaries. And this is exactly what the United Nations has done in its latest World Urbanization Prospects report.

Here, they have fundamentally revised their measurement methodology by using a new, so-called harmonized geospatial approach. If you'd like to nerd out on the specifics, you can do that here.

But one of the key takeaways is that this new methodology has resulted in a reordering of the world's largest urban agglomerations. At the top is now Jakarta, followed by Dhaka:

Previously, Tokyo was thought to be the world's most populous megacity, but it has dropped down to 3rd in this new report. And by 2050, it is forecasted to drop even further to 7th place:

As we spoke about yesterday, the world's economic center of gravity is rapidly shifting toward Asia. And that shows up in these charts.

I have a strong desire to visit the largest cities in the world. It's fascinating to see how such large urban clusters manage to organize themselves. There are always systems that naturally emerge to make things work, even if it feels chaotic on the surface.

I've only been to 3 cities from the 2025 chart, so I have my work cut out for me.

Cover photo by Rifki Kurniawan on Unsplash

We have spoken over the years -- here, here, and here -- about the centralizing and decentralizing forces that play out within our cities. Agglomeration economies, for example, are a centralizing force. There are real economic benefits to people and firms clustering together in cities.

However, there are also many decentralizing forces. Traffic congestion is one. And of course, the pandemic also proved to be a powerful one for many cities.

But the fact that we even have cities in the first place should tell you that the centralizing forces do tend to win out over the decentralizing ones. And a perfect example of this is Tokyo. Usually considered to be the largest metropolitan area in the world, Tokyo has about the population of Canada in one city region.

And here, the centralizing forces are so great -- even for families -- that the government actually pays people to relocate to places outside of Tokyo's 23 wards (and its immediately surrounding areas). Previously the maximum figure was ¥300,000 per child (~CA$3,056), but this has now been increased to ¥1 million per child (~CA$10,188).

A key driver of this is surely Japan's demographic problem (namely a shrinking and aging population base). But it doesn't change the fact that lots of people appear drawn to the world's largest city.

Following my recent post about the largest cities in the world (from 100 to 2015 CE), a number of you rightly pointed out that the data looked questionable. Where, for example, is Shanghai in this latest list of largest cities? So I think it's important that I do a follow-up post.

There are a number of nuances to consider when trying to measure urban populations. Perhaps the two most obvious are the geographic extent of each city (i.e. what urban boundary do you use) and the number of people living in informal settlements.

The UN recently estimated that there are some 1 billion people living in slums or informal settlements. That represents nearly a quarter of the world's urban population, which is a staggering number and a pressing global need. We desperately need more housing.

When it comes to measuring the size of an urban agglomeration, most of the studies that I have seen tend not to focus on municipal boundaries ("city propers") or metropolitan areas. The former is often based on arbitrary political boundaries and the latter often contains undeveloped rural land.

So for the purposes of this post, I'm going to go with Demographia's definition of "built-up urban area." They define this as being a continuously built-up area with one labor market and with no rural land. In their view, the world is either urban/built-up or rural. The built-up part is the lighted area that you would see on a nighttime satellite photo.

Given this definition, there are a number of interesting fringe cases. For example, contiguous/adjacent urban areas with more than one labor market get split up into multiple ones. This is the case in the US with the northeastern "megalopolis" that runs from Boston to Washington.

Conversely, if adjacent urban areas share a labor market and are linked together by similar commuting flows, then they get grouped into one urban area. This might be the case even if the area(s) straddle a national border. In this particular case, the free movement of people and goods would be another prerequisite.

With these definitions out of the way, below is another stab at sharing an accurate list of the world's largest megacities or built-up urban areas. This is one is by Demographia and there are a number of key changes compared to the last one I shared. Shanghai now features in the top 10. But Lagos drops down to number 20, which remains a bit of a question mark for me.

For a copy of Demographia's full report, click here. It looks at all urban areas with a population greater than 500,000 people (total is 985). Of course, if any of you have any other data sources that you think I should take a look at, feel free to share them in the comment section below.

It's not always as straightforward as it may seem to measure the size of a city or urban region.

There's the problem of which urban boundary to use. And then once you've landed on that, there's the additional problem of estimating how many people live within it. This can be particularly challenging when it comes to informal settlements, where there isn't reliable population data.

The most common approach is to use the continuous built-up area as the urban agglomeration, as opposed to any sort of "city proper" boundaries. And this is exactly what the United Nations has done in its latest World Urbanization Prospects report.

Here, they have fundamentally revised their measurement methodology by using a new, so-called harmonized geospatial approach. If you'd like to nerd out on the specifics, you can do that here.

But one of the key takeaways is that this new methodology has resulted in a reordering of the world's largest urban agglomerations. At the top is now Jakarta, followed by Dhaka:

Previously, Tokyo was thought to be the world's most populous megacity, but it has dropped down to 3rd in this new report. And by 2050, it is forecasted to drop even further to 7th place:

As we spoke about yesterday, the world's economic center of gravity is rapidly shifting toward Asia. And that shows up in these charts.

I have a strong desire to visit the largest cities in the world. It's fascinating to see how such large urban clusters manage to organize themselves. There are always systems that naturally emerge to make things work, even if it feels chaotic on the surface.

I've only been to 3 cities from the 2025 chart, so I have my work cut out for me.

Cover photo by Rifki Kurniawan on Unsplash

We have spoken over the years -- here, here, and here -- about the centralizing and decentralizing forces that play out within our cities. Agglomeration economies, for example, are a centralizing force. There are real economic benefits to people and firms clustering together in cities.

However, there are also many decentralizing forces. Traffic congestion is one. And of course, the pandemic also proved to be a powerful one for many cities.

But the fact that we even have cities in the first place should tell you that the centralizing forces do tend to win out over the decentralizing ones. And a perfect example of this is Tokyo. Usually considered to be the largest metropolitan area in the world, Tokyo has about the population of Canada in one city region.

And here, the centralizing forces are so great -- even for families -- that the government actually pays people to relocate to places outside of Tokyo's 23 wards (and its immediately surrounding areas). Previously the maximum figure was ¥300,000 per child (~CA$3,056), but this has now been increased to ¥1 million per child (~CA$10,188).

A key driver of this is surely Japan's demographic problem (namely a shrinking and aging population base). But it doesn't change the fact that lots of people appear drawn to the world's largest city.

Following my recent post about the largest cities in the world (from 100 to 2015 CE), a number of you rightly pointed out that the data looked questionable. Where, for example, is Shanghai in this latest list of largest cities? So I think it's important that I do a follow-up post.

There are a number of nuances to consider when trying to measure urban populations. Perhaps the two most obvious are the geographic extent of each city (i.e. what urban boundary do you use) and the number of people living in informal settlements.

The UN recently estimated that there are some 1 billion people living in slums or informal settlements. That represents nearly a quarter of the world's urban population, which is a staggering number and a pressing global need. We desperately need more housing.

When it comes to measuring the size of an urban agglomeration, most of the studies that I have seen tend not to focus on municipal boundaries ("city propers") or metropolitan areas. The former is often based on arbitrary political boundaries and the latter often contains undeveloped rural land.

So for the purposes of this post, I'm going to go with Demographia's definition of "built-up urban area." They define this as being a continuously built-up area with one labor market and with no rural land. In their view, the world is either urban/built-up or rural. The built-up part is the lighted area that you would see on a nighttime satellite photo.

Given this definition, there are a number of interesting fringe cases. For example, contiguous/adjacent urban areas with more than one labor market get split up into multiple ones. This is the case in the US with the northeastern "megalopolis" that runs from Boston to Washington.

Conversely, if adjacent urban areas share a labor market and are linked together by similar commuting flows, then they get grouped into one urban area. This might be the case even if the area(s) straddle a national border. In this particular case, the free movement of people and goods would be another prerequisite.

With these definitions out of the way, below is another stab at sharing an accurate list of the world's largest megacities or built-up urban areas. This is one is by Demographia and there are a number of key changes compared to the last one I shared. Shanghai now features in the top 10. But Lagos drops down to number 20, which remains a bit of a question mark for me.

For a copy of Demographia's full report, click here. It looks at all urban areas with a population greater than 500,000 people (total is 985). Of course, if any of you have any other data sources that you think I should take a look at, feel free to share them in the comment section below.