Cities have long been seen as the antithesis – or, at least, the absence – of nature. Yet in recent years, environmentalists started rethinking their long-held prejudices against urban areas. The rise of neighborhood-based environmental justice movements, beginning in the 1980’s, forced us to confront the human side of pollution and its relationship to urban poverty. The evolution of green building standards and advances in sustainable design helped us imagine an environmentally enlightened future for our offices and homes. The growing number of city-dwellers across the planet may have played the biggest role in our shifting perceptions of cities and nature. Moving “back to the land” and “living off the grid” could never be a tenable option for three and a half billion people. The result would end up closer to an explosion in suburban sprawl than a no-impact return to simpler times. Like it or not, we’ve realized that cities will have to figure into our schemes for a sustainable planet.

From April 11-30, we’re gathering up your ideas: from improving local parks and streets all the way up to rethinking whole systems, like transit and trash disposal. You can explore, discuss, and debate everyone’s ideas right here. In May, we’ll rally urban designers around the world to imagine the future of New York City based on your suggestions.