The urbanization of the world is not sustainable

We are more than 4 billion to live in cities. By 2050, 7 out of 10 humans will live in an urban area. Cities which have been spreading since the 1950s and which are exploding in the countries of the South. So how do you get around, eat, treat waste, manage water in cities that are constantly growing? The city is the right scale to innovate, but what models can we draw inspiration from?