orologio en CB01 OFFICIAL. At the start of the 20th century, just 10 percent of the world's population lived in cities. Today this figure already stands at 50 percent. By the end of this century, humanity will be an overwhelmingly urban species. The Urban Age has begun. But what should the cities of the future look like? How should they function? Urban planners are broadly in agreement that they should be green and efficient.