Visualizing 590 Cities

Visualizing 590 Cities

By now, you've probably heard: We're an increasingly urban species. Since 2008, more than half of us live in the world's cities; the end of urban sprawl is nowhere in sight. It is, of course, remarkable that for thousands of years, we've mostly lived in villages and on farms, in hamlets and sprawled across the countryside — yet sometime three years ago, we crossed a threshold where for the first time in history, we became mostly urbanites.

But buzzwords like "global urbanization" tend to lump together several trends that in themselves are far more fascinating. Which cities' populations are growing and which ones are shrinking? Are some global regions seeing more, and faster, urbanization than others? Can we compare trends across cities, and see how they change over time?

Answering these kinds of questions, one expects, would fill several pages in Wikipedia, or in graphical form, a hefty chunk of atlas.

Which is why we're so impressed with this stack flow chart, by Barcelona-based Bestiario that manages to pack all of those details into a single digital square. The visualization depicts the world's 590 most populous cities, sorted column by column according to their population size between 1950 and 2010, with projections for 2015, 2020, 2025, and 2050. By rolling over the lines you can highlight individual cities' growth trends. Tokyo, for instance, is the fat magenta bar at the top, a position it snagged from New York-Newark back in the 1950's. (Note that in the "normalized mode" cities are plotted relative to one another in each column, so the trend lines reflect relative, not absolute, changes in population — explaining why Tokyo is a flat line despite obviously having expanded since 1955.)

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Aside from being highly addictive, the rollover action on this chart provides numerous ways of exploring the data: One way is vertically. Pick any column and you can see which cities topped the "biggest" list in any given year. Compare two or more columns and you easily see how these rankings have changed over time. Check out these top 10 lists that we quickly drew up:

1950-  New York, Tokyo, London, Paris, Shanghai, Moscow, Buenos Aires, Kolkata, Beijing, Osaka-Kobe

2010-  Tokyo, Mexico City, New York, São Paolo, Mumbai, Delhi, Shanghai, Kolkata, Dhaka, Buenos Aires

2050-  Tokyo, Mumbai, Dehli, Dhaka, São Paolo, Mexico City, New York, Kolkata, Shanghai, Karachi

There are a number of interesting things going on here, but a few stand out: The American cities, especially New York, Mexico City, and Buenos Aires (yes, they're American cities) drop lower and lower in the list, and the European capitals Paris and London disappear from it entirely. Meanwhile, developing world cities climb the rankings, with behemoths like Mumbai and Delhi joined by newcomers Dhaka and Karachi. By 2050, the top 10 includes no fewer than 8 megacities from the developing world.

The rise of global South is even more dramatic if you explore the graphic horizontally, where it's possible to a quick sense of demographic trends by simply looking at curve shapes. You can see, for example, that São Paulo marches steadily upward, as do Mumbai, Al-Qahira, Manila, and Istanbul. In contrast, Paris, London, Detroit, Philadelphia, Moscow stairstep slowly, but incessantly downward. Another crop of cities — Lima, Mexico City, Osaka, and Seoul — like bell curves; in just the past 60 years, they've gone from rising stars to population has-beens, now being overshadowed by even-more-rapidly expanding urban hubs. Those newcomers are places like Lagos, Al-Khartoum, Kinshasa, and Dhaka, whose steep-climbing curves are the hallmarks of recent, explosive growth.

Clicking on the chart, rather than rolling over it, provides yet another way of gleaning information. Just toggle on a city and the visualization instantly highlights cities with similar growth curves — both on the flow chart itself, and, for the more geographically minded, also on a map. Now, you might expect that Washington D.C. would look much like New York and Toronto. But who knew that it would also bear striking resemblance to Cali, Colombia and Bordeaux, France? Beijing, unsurprisingly mirrors other Chinese cities such as Changsha and Baoton, but it also has twins in Douala, Cameroon and El Djazaïr, Algeria.

Indeed, one of the most striking patterns illuminated by this visualization is the symmetry amongst booming megacities within and across Africa, the Middle East, Southeast Asia, and China. A few minutes playing around with comparative clicking reveals that Bangalore looks much like a crop of 6 Chinese cities (Changchu, Guilin, Daquin, Hengyan, Hefei, and Changzhou); Karachi's dizzying growth parallels that of urban hubs in China, Cameroon, and Burma; Africa hosts an array of burgeoning metropolises all with growth curves fit for a billy goat: Lagos, Addis-Ababa, Lubumbasu, Kinshasa, and more.

In many ways, this burgeoning of developing world cities come as no surprise, as it mirrors what experts have long been saying about population growth on national and regional scales. National Geographic summed it up nicely last year in its Earth Pulse review:

"Virtually all of the expected population increase in the near future will come in developing countries, while the population of the more developed countries would be declining slightly, were it not for large-scale migration. In much of Europe, where explosive growth started with the industrial revolution two centuries ago, and in Korea, Japan, and elsewhere, national populations have stabilized or are starting to contract."

You can get a sense of these larger-scale population dynamics by focusing on the colors in this visualization. The Bestiario designers have assigned each city a color based on its regional geographic coordinates, with hue (for eg. blue, orange, pink) varying according to longitude and value (black to fully-saturated) changing with latitude. The following image summarizes the color palette:

If you can keep a single color, say, "purple," in mind while scanning down the chart, you can start to see a growth pattern emerge for Southeast Asia. Similarly, think "blue" for a view of the Indian region, and "turquoise" for Eastern Europe. Here's how 8 different regions of the world would look if mapped side by side:

In this view, we begin to see the very different dynamics of large cities in each region. Particularly striking is how Africa and Europe look almost like mirror images, as if existing at different moments in history. Zooming in on the United Kingdom reveals an unequivocal pattern:

Now, anyone with a even a vague knowledge modern European history will be able to take stab at the reasons for the UK's continued urban decay: post-Industrial social anomie; colonial upheavals; fertility rates of a wealthy country beyond the demographic transition.

Imagine building that kind of information into the visualization, to give a greater sense of backstory and socio-political context. What if, for example, clicking on a country in any given year generated a pop-up box with relevant news articles, Wikipedia entries, and/or photos from the web? (That model has given amazing depth to this this water visualization and also to this interactive view of earthquake history.)

Like the best visualizations, this one is effective because it's efficient — each color and shape, each hover and click conveys new information, not just eye candy. And like the best visualizations, while it answers a motherlode of questions, it also provokes new ones. We'd love, for instance, to know more about Why's and How's of megacity growth. Are we witnessing the results of new urbanites being born, or of mass human migration? Is migration mostly rural to urban, or do people hopscotch city to city? By getting more granular on these details, we'll be one step closer to understanding the complex economic, social, and environmental calculus that makes human move and multiply.

One final note: The Bestario team used data from the Nordpil database of large urban areas (1950-2050). According to Nordpil, the largest 590 cities on the planet all have more than 750,000 people. So "it's crazy," the designers say, "that if you take the 590 most populated cities, you don't reach half of the urban population of the world." That can be seen in the following graph:

What this says to us is two-fold: one, there a huge number of cities on the planet with less than 750,000 people (in fact, the designers tell us that as you widen the dataset to include less-populated cities, their number increases exponentially). Secondly, it signifies that even while we are an increasingly urban peoples, we are still very rural too! Just a hairs' breadth under half of humanity lives far from elevator shafts and the crush of 5pm traffic. Many of them are small-scale farmers, who fuel and feed the rest of us. We'd like to see this rural populace visualized as stunningly as 590 Cities gives us a view of our urban side.

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