City rankings are wildly abundant and as we’ve written before many of them have questionable criteria at best. Although there’s no shortage of “most livable cities” indexes there is little variation among most of them (the top listings often going to mid-sized cities in Canada Australia and Scandinavia) the common element frequently missing is the megacity. Though they can be some of the most sustainable places to live (thanks to dense land use and high transit usage) megacities are hard to find at the top of livability indexes.

David Roberts over at Grist has an answer to this problem: expand the focus. Roberts argues that what truly makes places livable is a larger notion in which sustainability should be viewed as one of the primary factors. Roberts points out that the common methods for improving sustainability – better technology and reduced consumption – are incomplete without looking at a major third factor: land use.

“Density is the sine qua non of sustainability” writes Roberts. “Generally speaking if you’re an American living in a suburban or rural area it doesn’t matter if you live in a green home own a Prius are vegetarian have a compost bin and backyard chickens — your footprint is bigger than someone living in an efficiency apartment in Manhattan.”

Recognizing that the appeal of Pastoralism (“a back-to-the-land romance” as he calls it) persists among many environmentalists Roberts claims that it is simply an out-dated and unrealistic notion.

“Big cities were horribly dirty and unpleasant for a very long time and that shaped generations of attitudes. It shaped a movement that came together around love of untouched wilderness and conservation of land and species” Roberts wrote.

“But density is the imperative. Pastoralism is only sustainable if you cut the global population down to about a tenth its current size and/or convince hundreds of millions of people to forego the amenities of modern life. Neither of those seem likely short of global catastrophe. More likely the future will be crowded and resource-strained. The only way past is through and that means putting our collective intelligence (and computing power) toward the conundrum of how to make it pleasant to live close to a bunch of other people and share a bunch of stuff with them.”

During much of the 20^th century the vision of livability was sprawl. In the 21^st century it’s urbanism.