By making "urban" synonymous with "city," we miss the realities of where we live and how our sprawling ways are changing the world.

Last month, the journal Science published a special issue examining the challenges and opportunities of an urbanizing world. Titled “Urban Planet” and featuring an image of clouds wafting across skyscrapers in Dubai, the issue opened with an eye-catching statistic: “More than half of the world’s people now live in cities.”

Of course, that number would be even more impressive if it were actually true.

“We don’t have 50 percent of the world living in cities,” says Karen Seto, a geographer at Yale University who studies urbanization trends. “A lot of these people are living in towns and small centers.” In other words, their surroundings are more urban than a rural village, but a far cry from Dubai.

The oft-cited statistic — or the idea behind it — began with a United Nations report released in 2007. It announced that by the following year, more than half the world’s population would be urban for the first time in history, and that such concentration was expected to rise to 70 percent by 2050. In 2014, the UN revised that trajectory slightly downward. The new calculation projected a 66 percent urban planet by 2050.

In both cases, to get those figures, the UN relied on data from each country about its urban population. One problem? Different countries have completely different definitions of what “urban” is. 

Table of Contents: Nature Special Issue "Urban Planet"

INTRODUCTION TO SPECIAL ISSUE

  • Cities are the Future by NICHOLAS S. WIGGINTON, JULIA FAHRENKAMP-UPPENBRINK, BRAD WIBLE, DAVID MALAKOFF: Rapid urbanization is overtaxing the planet, but it may not have to
  • Rise of the City, The geography of urbanization.
  • Roots of the Urban Mind,  by GREG MILLER:  The stress of living with strangers may have spawned cherished aspects of city life.
  • A Plague of Rats by WARREN CORNWALL: As more people crowd into urban slums, the risks posed by rodent-borne diseases are on the rise.
  • China Rethinks Cities by DENNIS NORMILE: After decades of reckless growth, the country revises its vision.
  • Vancouver's Green Dream by KENNETH R. WEISS: The city wants to dramatically shrink its environmental footprint, but obstacles loom.

REVIEWS

  • City-integrated renewable energy for urban sustainability by DANIEL M. KAMMEN, DEBORAH A. SUNTER: Emerging solutions to the water challenges of an urbanizing world by TOVE A. LARSEN, SABINE HOFFMANN, CHRISTOPH LÜTHI, BERNHARD TRUFFER, MAX MAURER

PERSPECTIVES

  • Transport solutions for cleaner air by FRANK J. KELLY, TONG ZHU
  • The ecological future of cities by MARK J. MCDONNELL, IAN MACGREGOR-FORS
  • Living in cities, naturally by TERRY HARTIG, PETER H. KAHN JR.
  • Meta-principles for developing smart, sustainable, and healthy cities by ANU RAMASWAMI, ARMISTEAD G. RUSSELL, PATRICIA J. CULLIGAN, KARNAMADAKALA RAHUL SHARMA, EMANI KUMAR
  • Hidden linkages between urbanization and food systems by KAREN C. SETO, NAVIN RAMANKUTTY
  • Building functional cities by J. VERNON HENDERSON, ANTHONY J. VENABLES, TANNER REGAN, ILIA SAMSONOV