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

Canadian geographer Mario Polèse's book, The Wealth and Poverty of Regions: Why Cities Matter, is not new. It was originally published in 2010. But it's perhaps a good follow-up to yesterday's post about the untethering of wealth. Here's an excerpt from a review of the book by Jeb Brugmann:

All cities, Polèse explains, share the same basic economic causes and effects. These are economies of localization (i.e., locating activities close together) and of urbanization (i.e., clustering lots of diverse activities together at scale). Polèse shows how these urban economies—usefully distinguished and defined in detail as economies of scale, proximity, diversity and concentration—combine with unique natural features and resource endowments, technology and infrastructure investments, national boundaries and market controls, and historical events to create quintessentially local and unique places. Every time he explains the status of another place—New York, London, Chicago, Paris, Montreal, the northern Mexico border, the North American west coast—he demonstrates again how the source code of geography combines with specific local and historical conditions to create a momentum of wealth or poverty.

The rich may have the means to tax-optimize through physical mobility, but the draw to established urban clusters remains strong, which is why it can be a challenge to stay away from them for more than 183 days. There is a "stickiness" to established cities that is the result of momentum and compounding over centuries.

Still, nothing is guaranteed, and there's only so much that can be done if you're swimming against a global landscape that is shifting away from you. Geography does matter. And today, the world's economic center of gravity is rapidly shifting toward Asia. This is good for some cities and bad for others.

Cover photo by Zhu Hongzhi on Unsplash

Most of us have heard of the so-called "Blue Zones." These are the parts of the world where there is an exceptionally high number of centenarians — people over the age of 100. We've talked about this topic before, covering the importance of things like diet, community, and constant moderate physical activity. But I would like to reiterate just how impactful our physical environments can be on our overall well-being.

The island of Sardinia is one of the world's Blue Zones. But it's not actually the entire island of Sardinia; it's a specific inner mountain region that is the Blue Zone. And in this region, at least two things are fascinating: First, the men have some of the longest average life expectancies in the world and second, the men live just as long as the women do. This is unique. Ordinarily, women outlive men. But not here.

The data overwhelmingly suggests that this outcome is the result of topography and employment. Because it is a mountainous region, the built environment is filled with steep inclines and staircases everywhere you go. The result is that even walking down the street to go to church or the grocery store results in organic moderate physical activity.

At the same time, the men in this region have historically worked as shepherds. This meant that work also involved walking up and down hills all day. Again, more organic moderate physical activity. Because of this, research has found very significant correlations between longevity and pastoralism, the average slope of the territory, and the average daily distance required to reach work. The steeper the better.

There's little mystery here. We know that more activity is better for us than less. The challenge is that we can't all live in bucolic mountain towns and chase sheep around all day. Modern society demands a lot of sitting and typing and vibe coding. We also have a market economy that is constantly looking for ways to make our lives more convenient so that we're able to do even more sitting around.

We try to compensate for this with gyms and other fixes (“Urban Cycles” cover image by Marcellus Hall):

But the better and more fundamental solution is organic moderate physical activity. Meaning, moderate physical activity that we don't have to actively seek out, and that is organically embedded throughout our everyday lives. It's best when it's a lifestyle. And this is one of the reasons why I view cities where walking and cycling are ingrained as a great luxury. All else being equal, these places are destined for better health outcomes.

If I look up my Apple Health data for 2025, there are very clear spikes in steps whenever I'm traveling. This makes sense. It's because I like going to places where I can walk around all day and be physically active. I can only sit on a beach for so long. But it's also ironic that modern life dictates that I have to go on vacation in order to be more active. That's not how Blue Zones work.

There is no greater luxury than our health. Without it, nothing else matters. And so I think it behooves us to make it a fundamental component of city building.

Cover photo by Valentina Uribe Posada on Unsplash