参考サイト1：Why Cities Matter
Consider that just two centuries ago, only 3 percent of the world’s population lived in cities. Today, it is exploded to more than half the world’s population.
Cities generate the wealth and improve living standards while providing the density, interaction, and networks that make us more creative and productive. They are the key social and economic organizing units of our time (of our time: 現代の), bringing together people, jobs, and all the inputs required for economic growth.
Cities are engines of innovation; their concentrations of talented and creative people promote and accelerate economic growth.
When we say ‘cities’, we really mean ‘metropolitan areas’. A ‘metro’ or metropolitan area encompasses not just a center city but its suburban rings.
Describe the different way we define and measure cities.
Nearly 85 percent of Americans live in metro areas, which produce 90 percent of the U.S.’s total economic output (economic output : 経済生産高) and 85 percent of its jobs. Across the world, metros with populations of more than one million people account for more than half the world’s economic output, while housing roughly one in five of its people.
As they grow bigger, many of these metros are morphing into mega-regions.
Great cities and metropolitan areas grew together into something even bigger.
If our cities are our most powerful engines of growth, they are also greener and more environmentally efficient than suburbs and small towns. Multi-family dwellings (multifamily dwelling: た世帯住宅・アパート) that share walls are easier to heat than detached single family houses; density discourages car use and promotes mass transit and walking. Our cities are safer, too. Crime is down to its lowest level in 40 years, especially in America’s biggest cities. Part of the reason lies in better policing, but much of it lies in growing diversity and improving conditions.
Housing prices (housing price: 住宅価格) have risen and economic and class divides have worsened. The growing divides between cities and regions.
And then there are the countless millions who fill the increasingly disconnected and truly disadvantaged mega-cities of the Third World. More than one billion people live in their slums. Even though conditions there are better than in the rural countryside, they desperately need rudimentary water and sewer infrastructure, basic housing and schools, and the ability to protect their citizens, especially school-age children.