This article was originally published in Metropolis Magazine as "When It Comes to Sustainability, We're Ranking Our Cities Wrong."

A recent article published in Nature makes a bold claim: we're analyzing our cities completely wrong. Professors David Wachsmuth, Aldana Cohen, and Hillary Angelo argue that, for too long, we have defined sustainability too narrowly, only looking at environmental impact on a neighborhood or city scale rather than a regional or global scale. As a result, we have measured our cities in ways that are inherently biased towards wealthy cities, and completely ignored the negative impacts our so-called "sustainable," post-industrial cities have on the rest of the world.Metropolis editor Vanessa Quirk spoke with Professor Wachsmuth to learn more about the unintended knock-on effects of going "green," the importance of consumption-based carbon counting, and why policy-makers should be more attentive to the effects of "environmental gentrification."

Videos

With the first ever World Cities Day taking place on Friday, the Guardian is partnering with UN Habitat for the Cities Day Challenge, a day-long competition where representatives of 36 cities around the world will present their best city ideas, with the winner being selected for an in-depth article in the Guardian. Judged by Ivan Harbour of Rogers Stirk Harbour + Partners, Toronto City Planner Jennifer Keesmaat; Anna Minton, Dan Hill, Usman Haque and Adam Greenfield, the Guardian will be live-tweeting the entire day.

They are also reaching out to readers to "share your photos, videos and stories of something brilliant that your city does better than any other," some of which they will feature throughout the day. You can follow this link to contribute - or read on after the break as we take the opportunity to round up some of the biggest city ideas that have passed through the pages of ArchDaily.

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There's no doubt about it - cycling in cities is a big deal these days. But, while cycle lanes and bike-sharing schemes are all well and good for our cities, the cycling revolution hasn't yet brought us many examples of beautifully designed infrastructure to gawp at. This article, originally printed on The Dirt as "Do Elevated Cycletracks Solve Problems or Just Create More?" discusses two seemingly similar examples of high profile cycling infrastructure, examining why one is a success and the other a non-starter.

This year, two designs – one proposed and one built – for elevated cycletracks, which create bicycle highways above street level, have gained considerable media attention. They highlight questions at the heart of urban design: Should cities blend or separate transportation options? How can cities best mitigate the hazards created when cars, bikes, mass transit, and pedestrians mix? How can cities create low-cost transportation networks in increasingly dense urban cores?