If you wanted capture more than 55% of the world’s population within a circle with a radius of 4,000 km, which city would you place at its epicenter? It is what was asked in 2013, Ken Myers, a user of Reddit. Within days he calculated that his Valeriepieris circle (from his account name on the platform), a circular region on a two-dimensional map, centered on the South China Sea and with a radius of about 4,000 km, contained more than half of The world population.
More people lived within that sixth of the world’s land area than outside. That representation, however, left open another interesting question: “Where is the smallest circle that can be drawn on our planet that contains at least half of the population Then came Danny Quah of the London School of Economics in 2015, who analyzed the circle in more detail under the title The smallest group of people in the world.
Recognizing that the Valeriepieris circle is not actually a circle (it was drawn on a two-dimensional map rather than a globe) and is based on data that has become outdated, now cartographer Alasdair Rae has investigated and discovered what he calls The Yuxi Circle, the most densely populated area in the world. Rae circled around 1,500 cities around the world to find out how many people lived within a radius of 4,000 km, just like the original Valeriepieris circle. He based his calculations on WorldPop data from 2020.
Of the 1,500 circles Rae calculated for, 148 contained populations of 4 billion or more. He found examples in Asia, including China, Myanmar (Mandalay), Laos (Vientiane), Bangladesh (Chattogram), India (Agartala), Bhutan (Thimpu), and Vietnam (Hanoi), to name a few. But of all of them, Yuxi, a city in China’s Yunnan provincehas the largest population within a radius of 4,000 km: 4,320 million.
That is, the circle encompasses more than 55% of the world’s population, despite including desolate areas such as the Taklamakan desert, the Tibetan plateau, Mongolia and southern Siberia. There is more than one Yuxi in China, but the one on the map is in Yunnan province and has a population of around 2.5 million. Obviously when you draw a simple 4,000 km buffer you always get a lot of sea, so he also tried to see what kind of ellipse he could draw around Yuxi that still included more than half of the world’s population.
Densely populated areas around the world
Rae’s search for densely populated groups also turned up notable circles beyond Asia. She circled cities like Cairo, Paris, and Mexico City. Going around Hanoi, she obtains a population of 4,270 million (54% of the world population). Around Cairo you get a population of 2.29 billion. This circle reaches most of Europe and still contains populated areas of India, Pakistan and Africa.
Comparatively, going around Paris you get a population of 1,190 million. This Eurocentric circle contains large bodies of water and sparsely populated islands like Iceland and Greenland.
Across the Atlantic, going around Mexico City, you get a population of 730 million. It is significantly smaller than the other circles, since the total population of America is concentrated in just three countries, the US, Mexico and Brazil (not included in this circle).
Note: Note that the white lines on flat maps are equidistant circles, but will only appear as circles when plotted on a globe.
Overlaying countries on others
After her investigation, Rae still wanted more. And she started thinking, “what if someone built a tool like True Size Of but then combined it with NASA’s SEDAC Population Estimation Service?” It occurred to her thus to take the form of a country, overlay it somewhere else in the world and get the population inside it. He made a little attempt with the lower 48 US states, which he moved south and scaled geodesically, and then calculated the population within them when he placed them above China and India.
He also did this with the US flipped horizontally, just because the west coast fits reasonably well with the east coast of China.
The Valeriepieris Circle
It’s worth noting that Valeriepieris’s circle also inspired other people to look at population density in different ways. In 2015, Danny Quah of the London School of Economics took a closer look at Valeriepieris’ circle and was inspired to find the smallest circle with more people living inside than outside. He determined that a circle with a radius of 3,300 km centered near Mong Khet, Myanmarwas “the most compact group of people in the world”.
He developed an algorithm to answer that question. With the help of Ken Teoh, a Wharton School student showed that Ken Myers’ guess turned out to be very similar to his. Of course, populations in different parts of our planet change over time, but in 2015, using population data at 100 km resolution at the Earth’s surface, the smallest circle of our planet containing most of the world was that circle centered near Mong Khet, Myanmar, with a great circle distance of 3,300 km.
Maps: Alasdair Rae | Danny Quah | Ken Myers