Seoul, South Korea's capital, at night. (SeongJoon Cho/Bloomberg)

As I mentioned last week, college graduates are increasingly sorting themselves into high-cost, high-amenity cities such as Washington, New York, Boston and San Francisco, a phenomenon that threatens to segregate us across the country by education. This clustering of the well-educated — who are drawn to cities with a high quality of life and good jobs, further pushing up the cost of rent there — isn't limited to the United States, though.

Ugne Saltenyte, an analyst at the market research firm Euromonitor, recently calculated that 24 percent of the world's population over 15 years of age and with the equivalent of a two-year degree or more is concentrated in the world's 100 largest cities. These same 100 cities — Saltenyte is counting full metropolitan areas here — are home to just 11 percent of the world's total population.

In these cities, residents with higher education account for 21 percent of the population over 15, a number that's increased from 18 percent as recently as 2005. This suggests that these cities may be both investing more heavily in education and luring educated workers from elsewhere. Locally, the educated share of the over-15 population is particularly high in the Washington/Baltimore metro region, San Francisco and Boston, even by global standards:

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Metropolitan New York, Chicago, Philadelphia, Miami, Los Angeles, Phoenix and Houston are also included on this list.

In the coming years, developing countries are expected to heavily invest in education, further expanding the global ranks of the educated. Worldwide, Saltenyte calculates that 704 million people in 2013 had some higher education. Back in 2005, that number was 518 million
(if you really want to get in the weeds on Saltenyte's metric, she's including the International Standard Classification of Education levels that roughly correspond to an associate's degree, a bachelor's and a master's).

As the world's educated population swells, though, the benefits of that education could become even more concentrated.