In may ways, this recent article by Brian Potter about how fast cities can grow, feels intuitive: Small cities tend to grow faster than big cities (on a percentage basis) and, as cities get bigger, their growth rates tend to decline. It is, however, still interesting to see the data behind this intuition:

A city of less than 100,000 might be able to have growth rates of 10-20% or more, and cities of up to 3-400,000 can potentially have growth rates in the neighborhood of 10-15%. Potential growth rates tend to fall as cities grow larger, and cities above 1 million people almost all grow at less than 10% per year, and usually less than 5% per year. The US, the Middle East, Southeast Asia, Africa, and South America all seem to have followed this basic pattern, assuming the data is reliable.

It is also a good reminder just how much of an outlier China is:

Unsurprisingly, since 1950, Chinese cities have mostly exhibited higher growth rates than US cities. Only around 12% of US data points are above a 5% growth rate, whereas for China this is close to 50%. China also has 2.5x the fraction of cities growing above 10% per year, and 3.3x the fraction of cities growing above 15% per year.

And some cities are outliers even within China. The most notable here is Shenzhen, which saw enormous growth after it became China’s first special economic zone in 1980. At a population of around 200,000, Shenzhen was growing at 35% annually, and it was still growing at over 20% annually when its population crossed 2 million.

Just imagine these numbers compounded. Even small variances can result in significantly different outcomes over time:

New York’s growth rate, however, declined less than Los Angeles or Chicago as the city grew larger. At around 3.5 million people, New York was still growing at over 3% per year, compared to less than 1% for LA and Chicago. This may not sound like much, but it's the difference between doubling in size every 23 years vs. every 70 years.

Now here's what I'm wondering after reading the article: Should we be thinking of city size as the single most important factor in determining urban growth? Because my mind immediately went to population densities, zoning controls, and other factors that might constrain or encourage growth.

But the data seems to suggest that, for many cities, this doesn't seem to matter over the long run. It is as simple as saying, "this city has X number of people and so it's more than likely growing at somewhere around Y% per year."

That said, what's up with China? What is it that allows a city of 2 million people to still grow at over 20%? Is it the sheer influx of people migrating from rural to urban areas? Or is it that you need a one-party authoritarian state to really clear the way for growth?

As cities get bigger there does appear to be a natural tendency toward slower growth. Part of this is the low base effect. But the declines are not always consistent and there are meaningful outliers. I am now curious to know what, for the most part, causes these differences.

Since 2012, a team at New York University has been working on something called the Atlas of Urban Expansion. What they are doing is collecting and analyzing data related to the quantity and quality of urban growth around the world. Everything from population densities to how well the streets were laid out during each geographic expansion.

The Atlas defines a city as having at least 100,000 people, which is a commonly used benchmark. According to this definition, there were 4,245 cities on the planet as of 2010. Included in their study is a representative sample of 200 of them, all of which can be found here.

They are also, rightly, looking at each city in terms of its extrema tectorum -- the limits of its built-up area. This is as opposed to using administrative boundaries, which wouldn't be as relevant in a study like this.

I really like the animations that they created depicting urban growth from 1800 to 2014, because they show: (1) where each city started (the dark nucleus); (2) how different urban shapes emerge as a result of geography, transport, and other factors; and (3) how land consumptive many of our cities have become in recent years.

Image: Atlas of Urban Expansion

Shaping Cities in an Urban Age is the third book to come out of the London School of Economic's Urban Age project. It was published last fall. The first two titles were, Living in the Endless City (2011) and The Endless City (2007).

If you're familiar with the first two publications, you'll know that these books are heavily illustrated. Lots of maps, charts, and diagrams. So they make great coffee table books. But they're also filled with insightful essays -- this one has 37 of them.

In this particular book the focus is on the following:

"It identifies current trends that are making cities more fragmented, less equitable and environmentally more damaging, and argues powerfully for a more integrated social, environmental and spatial approach that can inform and inspire city-makers that are shaping an increasingly urban world."

I am sharing this with all of you today because I have always really enjoyed these books. They have a way of quickly putting things into perspective globally.

Around 2.5 billion more people are expected to live in an urban agglomeration by 2050. And 90% of this growth is expected to happen in just two places: Asia and Africa. This is an unprecedented shift that will obviously create many challenges and many opportunities.

This book is about that.

Image: Phaidon

In may ways, this recent article by Brian Potter about how fast cities can grow, feels intuitive: Small cities tend to grow faster than big cities (on a percentage basis) and, as cities get bigger, their growth rates tend to decline. It is, however, still interesting to see the data behind this intuition:

A city of less than 100,000 might be able to have growth rates of 10-20% or more, and cities of up to 3-400,000 can potentially have growth rates in the neighborhood of 10-15%. Potential growth rates tend to fall as cities grow larger, and cities above 1 million people almost all grow at less than 10% per year, and usually less than 5% per year. The US, the Middle East, Southeast Asia, Africa, and South America all seem to have followed this basic pattern, assuming the data is reliable.

It is also a good reminder just how much of an outlier China is:

Unsurprisingly, since 1950, Chinese cities have mostly exhibited higher growth rates than US cities. Only around 12% of US data points are above a 5% growth rate, whereas for China this is close to 50%. China also has 2.5x the fraction of cities growing above 10% per year, and 3.3x the fraction of cities growing above 15% per year.

And some cities are outliers even within China. The most notable here is Shenzhen, which saw enormous growth after it became China’s first special economic zone in 1980. At a population of around 200,000, Shenzhen was growing at 35% annually, and it was still growing at over 20% annually when its population crossed 2 million.

Just imagine these numbers compounded. Even small variances can result in significantly different outcomes over time:

New York’s growth rate, however, declined less than Los Angeles or Chicago as the city grew larger. At around 3.5 million people, New York was still growing at over 3% per year, compared to less than 1% for LA and Chicago. This may not sound like much, but it's the difference between doubling in size every 23 years vs. every 70 years.

Now here's what I'm wondering after reading the article: Should we be thinking of city size as the single most important factor in determining urban growth? Because my mind immediately went to population densities, zoning controls, and other factors that might constrain or encourage growth.

But the data seems to suggest that, for many cities, this doesn't seem to matter over the long run. It is as simple as saying, "this city has X number of people and so it's more than likely growing at somewhere around Y% per year."

That said, what's up with China? What is it that allows a city of 2 million people to still grow at over 20%? Is it the sheer influx of people migrating from rural to urban areas? Or is it that you need a one-party authoritarian state to really clear the way for growth?

As cities get bigger there does appear to be a natural tendency toward slower growth. Part of this is the low base effect. But the declines are not always consistent and there are meaningful outliers. I am now curious to know what, for the most part, causes these differences.

Since 2012, a team at New York University has been working on something called the Atlas of Urban Expansion. What they are doing is collecting and analyzing data related to the quantity and quality of urban growth around the world. Everything from population densities to how well the streets were laid out during each geographic expansion.

The Atlas defines a city as having at least 100,000 people, which is a commonly used benchmark. According to this definition, there were 4,245 cities on the planet as of 2010. Included in their study is a representative sample of 200 of them, all of which can be found here.

They are also, rightly, looking at each city in terms of its extrema tectorum -- the limits of its built-up area. This is as opposed to using administrative boundaries, which wouldn't be as relevant in a study like this.

I really like the animations that they created depicting urban growth from 1800 to 2014, because they show: (1) where each city started (the dark nucleus); (2) how different urban shapes emerge as a result of geography, transport, and other factors; and (3) how land consumptive many of our cities have become in recent years.

Image: Atlas of Urban Expansion

Shaping Cities in an Urban Age is the third book to come out of the London School of Economic's Urban Age project. It was published last fall. The first two titles were, Living in the Endless City (2011) and The Endless City (2007).

If you're familiar with the first two publications, you'll know that these books are heavily illustrated. Lots of maps, charts, and diagrams. So they make great coffee table books. But they're also filled with insightful essays -- this one has 37 of them.

In this particular book the focus is on the following:

"It identifies current trends that are making cities more fragmented, less equitable and environmentally more damaging, and argues powerfully for a more integrated social, environmental and spatial approach that can inform and inspire city-makers that are shaping an increasingly urban world."

I am sharing this with all of you today because I have always really enjoyed these books. They have a way of quickly putting things into perspective globally.

Around 2.5 billion more people are expected to live in an urban agglomeration by 2050. And 90% of this growth is expected to happen in just two places: Asia and Africa. This is an unprecedented shift that will obviously create many challenges and many opportunities.

This book is about that.

Image: Phaidon