Every day for the next 35 years, an average of 170, 000 people will move to, or be born 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, building materials, transportation, and land can be used super - efficiently.

Except cities aren't always the super - compact 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 people 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 maintain 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, more energy and more stuff per person.

We could reverse this trend by getting rid of the 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 or zoning of homes and businesses separately push growth outward.

So policies allow us to influence the shapes 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.

So, in cities, as in life, we have a choice : sprawl or grow tall.