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All in the City Family: the Network of Sister Cities

If you ever look up a city on Wikipedia, you will be treated with a section near the bottom of the page of a list of all the sister cities of that place—a list of partnerships between local governments that is geared towards some sort of economic and cultural exchange.

On the individual level, these partnerships are interesting but often seem a bit capricious: While I am unfamiliar with this process, I imagine that there are a whole host of distinct factors that contribute to how cities choose each other. But what happens if we zoom out and examine the network of sister city relationships? Do any patterns emerge?

A team of researchers at Barcelona Media set out to do just that. In a paper posted to the arXiv, they scraped the sister city data from Wikipedia and constructed a network based on over 15,000 pairs of sister cities (a total of about 11,000 distinct cities are in the dataset).

They discovered that this network is highly assortative: in other words, cities that have lots of connections are more likely to be sister cities with those cities that also have lots of connections. This is similar to social networks, where those who are popular are more likely to also be connected to others who are popular.

They also examined the ranking of cities in terms of connectivity as well as their centrality. And they found something great: “Saint Petersburg, often referred to as the geographic and cultural border of the West and East, is the most connected and also most central sister city.” Exploring this further, they examined the communities of cities that arise from their pattern of connectivity, and found four distinct somewhat regional clusters (seen below):

The largest one (in violet) includes the USA, Spain and most South American, Asian, and African countries. The second largest (in green) is composed of Eastern-European and Balkan countries: Turkey, Russia, and Poland are the most linked among them. The third cluster (in red) consists of Central and Western-European countries and some of their former colonies. It is dominated by Germany, UK, France and the Netherlands. Finally, the smallest cluster (in cyan) mainly consists of Nordic countries.

Intriguingly however, through further analysis, they find that overall geography and distance matter very little. This can be seen in the vast geographic spread of the largest cluster above. And while the authors argue that this heralds the long-awaited death of distance due to technology, I think this is simply due to the fact that cities in general simply desire to have geographically diverse “sisters.”

Either way, I look forward to seeing more of this kind of network: one that combines geography with political connections.

Top image:prayitno/Flickr/CC