in, cities in the developing world, mostly in fast-growing areas in Asia and Africa.

And there’s a lot to love about cities: they’re chock-full of jobs, art, jobs, community,

a small fortune in coins tossed into public fountains — and jobs! Cities can be good

for the planet, too - their compact nature means that water, power, transportation, building

materials, and land can be used super-efficiently.

Except cities aren’t always the supercompact islands of utopian awesome we sometimes imagine.

That’s because they’re usually made up of urban cores surrounded by less dense residential,

commercial, and industrial zones that sprawl on and on and on and on and on and on and

on and on and on…

Many of us may think of the suburbs as leafy-green lanes lined with picket fences and giant slobbery

dogs, but suburbia comes in many forms. And people in suburbs of all types gobble up more

energy, water and other resources and emit more pollutants than those in taller, denser

urban neighborhoods. They travel further to work and school, have more cars and drive

them further, heat and cool bigger homes, and tend bigger yards, negating the compact

efficiency of the dense urban cores they surround.

So suburb-ringed cities with low overall densities are much less efficient than those that are

tightly-packed. And unfortunately, cities around the world are expanding twice as fast

in area as they are in population, using up more land and energy and stuff per person.

We could reverse this trend by getting rid of resource-hungry suburban sprawl altogether.

But that just isn’t how cities tend to develop organically. In reality, wide highways and

cheap gas tend to encourage more cars and commuters, and height limits on buildings

and separate zoning of homes and businesses push growth outward.

So policies allow us to influence the shape of our cities, for bad or good. Investing

in mass transit and boosting gas prices encourages people to ditch their cars and live closer

to each other, while mixed zoning laws allow them to work and play closer to home. And

when people live densely, they use resources less intensely.

In cities - as in life - we have a choice: sprawl or grow tall.