Although they take up only about 3 percent of the planet’s usable land, our global cities house some 55 percent of the world’s people—and by mid-century, this number is expected rise to 68 percent. At the same time, Earth’s population is projected to grow to somewhere around 9.8 billion people, leading to a total of 6.6 billion urban citizens by 2050. Our urban centers will face mounting pressures as a result.
