Megacities grab the headlines, but they are home to only a minority of urban residents: about one in eight, according to the UN. Nearly half of the world's city dwellers live in places with fewer than 500,000 people. And under UN projections, most of the more than 15,000 cities expected by 2050 will have fewer than 250,000 residents.
That's the estimate from a WHO-led study published in The Lancet in 2024, covering the half-century since the Expanded Programme on Immunization was launched in 1974. It works out to about six lives saved every minute, mostly infants. The measles vaccine alone accounts for around 60% of those lives.
According to the World Gold Council, about 216,000 tonnes of gold have been mined in all of human history. Because gold is so dense (19.3 tonnes per cubic metre), it would fit in a cube about 22 metres on each side, roughly the height of a seven-storey building. Strikingly, about two-thirds of it has been mined since 1950.