Yerba Buena Center for the Arts (701 Mission St., San Francisco)

In this era of economic collapse, climate change and so many forms of unrest, it can sometimes be difficult to be optimistic. But we don’t always have the luxury to choose: “As an architect, if you’re not optimistic, you’re not going to be able to survive professionally, so you have to believe in the future,” says British architect Sir Norman Foster during Urbanized, a documentary that shows just how much is at stake in the development and survival of cities.

Urbanized, the final film in Gary Hustwit’s “design trilogy,” which also includes Helvetica and Objectified, screens at Yerba Buena Center for the Arts in San Francisco from November 4 through 10.

Urbanization is central to the challenges we face today, and this will only intensify, as the film explains: over half the world’s population now lives in an urban area, and 75% will call a city home by 2050. This is astonishing, historically unprecedented growth. Such rapid change brings many considerations, as cities must balance issues pertaining to housing, mobility, public space, civic engagement, economic development and environmental policy.

Architects like Sir Norman Foster, then, are clearly not the only players in the creation and sustainability of cities. Urbanized looks at how architects, planners, policymakers, builders, scholars, journalists, activists and ordinary citizens work together to build, design, shape and improve our cities.

Though optimistic, the film does not shy away from the severity of the challenges ahead. To the contrary, Urbanized examines how people have approached these issues in innovative ways: from Bogota’s investment in public transportation infrastructure, to urban gardening in Detroit, Copenhagen’s vibrant bicycle culture, violence prevention in a South African township and New York’s High Line.

A film that challenges us to think critically and work together, Urbanized frames a global discussion on the future of cities. For more information: http://www.ybca.org/urbanized