Distance to Next Closest City with over 1 Million People

Our analysis of the world's 400 cities with at least one million people (according to the UN Statistical Division's population of cities) found that the average large city is 235km from the next closest city of at least one million. The distribution of this data is shown below:

What are the closest city pairs?

Cairo / Giza at 4km

Manila / Caloocan at 6km

Kinshasa (DRC) / Brazzaville (Republic of Congo) at 8km closest foreign cities

What are the most remote cities?

Auckland is 2,161km from Sydney (note Sydney is only 714km from its closest big city, Melbourne)

Perth is 2,136km from Adelaide (note Adelaide is 654km from Melbourne)

What are the closest city pairs in each continent?

Africa: Cairo (Egypt) / Giza (Egypt) at 4km

Cairo (Egypt) / Giza (Egypt) at 4km Asia: Manila (Philippines) / Caloocan (Philippines) at 6km

Manila (Philippines) / Caloocan (Philippines) at 6km Australia and Oceania: Melbourne (Australia) / Adelaide (Australia) at 654km

Melbourne (Australia) / Adelaide (Australia) at 654km Europe: London (United Kingdom) / Birmingham (United Kingdom) at 163km

London (United Kingdom) / Birmingham (United Kingdom) at 163km North America: Guadalajara (Mexico) / Zapopan (Mexico) at 8km

Guadalajara (Mexico) / Zapopan (Mexico) at 8km South America: Barranquilla (Colombia) / Cartagena (Colombia) at 101km

What are the two closest foreign cities of at least 1 million?

The capital of the Democtratic Republic of Congo, Kinshasa, is only separated from the capital of the Republic of Congo, Brazzaville, by the Congo River. The distance between the two city centers is about 8km (although at the closest points, they are about 4km apart). Interestingly, the fastest and safest way to get between the two cities is a five minute flight (scheduled twice per week). [source]

How are there odd numbers of cities in a grouping - should they not be even? (e.g. there are 7 cities in North America that are less than 25km to each other)

City A may be closest to City B, but that does not mean that City B is closest to City A. In the case of North American cities less than 25km to each other, 3 of those cities are Mexico City and two other cities in the Mexico City metropolitan area, Netzahulacoyotl and Ecatepec.

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