Geography Reference
In-Depth Information
nated as “metropolitan,” because these areas held a city of at least i fty thou-
sand people. Another 20 percent were deemed “micropolitan” on account of
their economic and social connections to cities of between ten thousand and
i fty thousand people. Our proximity to cities gentrii es nearly half of the U.S.
national land base with well-tended lawns and gardens, public parks and rec-
reation areas, and the infrastructure of transportation, communication, and
energy. Worldwide, our coasts are densely settled, but even here, tree cover
can be substantial. Currently, one-quarter to one-third of most urban regions
around the world are covered with a canopy of trees or other natural greenery.
Metropolitan areas in the United States contain an estimated seventy-i ve bil-
lion trees that shade a third of the area. These “lungs of the city,” which pro-
duce oxygen and clean our air while providing essential habitat for other
species, will be at risk in the future.
Agricultural lands i ll in around our settlements and carpet much of east-
ern Europe, midwestern North America, Central America, and South Amer-
ica. One-third of Earth's land, and a full 40 percent of the United States, is
farmed—far more than we occupy with our villages, towns, and cities. Parts
of Africa, Australia, South America, and the Arctic remain wild and sparsely
settled. Antarctica is a wilderness, but today this is the exception.
Most demographers expect our growing population to lead to more cities,
especially moderately sized ones, widely distributed across the planet. In the
United States, a million more acres become urban each year. As Harvard ecol-
ogist Richard Forman puts it, an urban tsunami is on the horizon. For many,
the l ood has already hit and the swimming is tough; one-third of all urban
residents live in slums. When did this vast urbanization happen?
Five to six thousand years ago our ancestors in Mesopotamia and Syria created
the world's i rst cities. As early populations rose and fell with environmental
