News reports tell of a city that will rise in the New Mexico dessert, 20 miles square, where no humans will live. Instead, the city will be a model for designing and testing renewable energy systems, transit plans, and other technological innovations. Building a city from scratch may seem like an out-there plan, but it's a plan that has sparked the interests of investors, inventors, and architects many times. If you could start from scratch, without the hindrances of our built environment, what would your urban dream look like? Each answer reflects the particular hopes and values of those who design it; many recent proposals focus on creating a place that will run on more renewable energy and require less driving and commuting.

Below, a look at some cities-from-scratch plans and realities, some of which are home to thousands today, and others that, particularly in the wake of the global economic slowdown, will never make it off the page.