The brightest stars of this superb documentary are BogotĂĄ, Detroit, Copenhagen, Mumbai, and Santiago. The less bright ones are BrasĂ­lia, Rio de Janeiro, Cape Town, Beijing, New Orleans, and New York City. What distinguishes the brightest from the rest is not the city itself but the person who speaks for it. Each city has a main spokesperson—sometimes it's a mayor, other times a designer or community activist. If this spokesperson has a way of thinking that's passionate and magical, then the city spoken for ("represent, represent") shines brightly. If the spokesperson's thinking is simply interesting, then the city is not as dazzling. This slickly edited, scored, and photographed documentary—directed by Gary Hustwit, the man behind 2007's Helvetica and 2009's Objectified—really comes down to the issue on the mind of every urban planner: sustainability. How will cities in the near future be able to support their ever-increasing human populations? People are not leaving cities—they are moving into them, even if it means living in filthy slums, which is often the case. The documentary looks at different cities to see how each is coping with the rapid urbanization of the human race. "The only way to solve traffic jams is to restrict car use," says former BogotĂĄ mayor Enrique Peñalosa. "And the way to restrict car use is to restrict parking. But people seem to think parking is a right to be included in the UN's fundamental charter." Peñalosa, as you can see, has no love for cars. For him, parking is your problem, not the city's. The city's main problem is the public (the poor and the rich), and public transportation happens to solve a large part of the city's main problem.

The city also loves its citizens to use bicycles. "High-quality infrastructure increases the social status of bicycles," explains the former mayor as he cycles around like our mayor. "Before we had networked bikeways, low-income people were ashamed to use bicycles. But with a high-quality bikeway, it shows them that the city takes a person who spends $30 on a bicycle as seriously as a person who spends $30,000 on a car."

And it is here that we reach the most profound thinking in this documentary. Urban planning is about finding ways to better express democracy. A city that blocks democracy is one that gets more and more clogged with traffic jams. For a city to flow smoothly, to work for all inhabitants, it must have a design that's inherently egalitarian. Sustainability is not possible without a vibrant democracy. recommended