Broad patterns of the urban-region set 137(Canberra), though, like land masses, they are skewed to the northern hemi-
sphere. Elevations range from nearly sea level (Bangkok, Philadelphia) to
2200 m (Mexico City); the median is 116 m. Average annual temperature ranges
from− 2 ◦C(Ulaanbaatar) to 28◦C(Bamako), while nearly 60 % of the cities fall
between 10 and 20◦C. Average annual precipitation ranges from 3 cm (Cairo) to
274 cm (Iquitos); only five places record <50 cm and only four places >155 cm.
Latitude and elevation are central determinants of average temperature and
precipitation, which primarily determine the natural vegetation type for a
region. Of the world’s major vegetation types, no cities chosen are in tundra
or boreal forest (taiga). Cities are reasonably well distributed over the six major
vegetation types present: six inboreal--temperate transition forest(Berlin, Stockholm,
Ottawa, Portland, Moscow, Sapporo); eight intemperate deciduous-evergreen forest
(London, Nantes, Chicago, Philadelphia, Atlanta, Beijing, Seoul, Kagoshima); five
intropical rainforest(Iquitos, Bangkok, Kuala Lumpur, Cuttack, Samarinda); five
inMediterranean-type woodland(Rome, Barcelona, San Diego/Tijuana, Santiago,
East London); six insavanna-woodland(Mexico City, Brasilia, Tegucigalpa, Nairobi,
Bamako, Canberra); five ingrassland(Bucharest, Edmonton, Abeche, Ulaanbaatar,
Erzurum); and three indesert-woodland(Cairo, Tehran, Rahimyar Khan).
City location relative to water bodies is particularly important in urban
regions. Fourteen cities are on a single major river, and another four are on
the intersection of major rivers. Four cities are on the shore of a lake or reser-
voir, one associated with a river and one with a sea/saltwater bay. Four are on a
seacoast and one on a saltwater bay. Ten cities have no adjacent major surface
waterbody, though all have streams or seasonal water flows in gullies. Again a
wide range of city and water-body locations is included.
Cities were chosen so their urban region would be minimally affected by
another nearby city. Thus 13 cities have no nearby major city (>250 000 popula-
tion) within 200 km, and another 19 have no city within 100 km. In one case
(Kagoshima) the nearest major city is smaller in population and 90 km away. In
theother five cases (Mexico City, Cairo, Seoul, Tehran, Stockholm) with closer
nearby cities (20--80 km distant), the other major city is much smaller.
The perimeter and area of metropolitan areas vary from tiny Abeche to huge
Chicago (Table 5.1). In general, US cities have the largest metro areas, both in
perimeter and area, though the much-more-populous London and Moscow have
long perimeters, and London, Moscow, Mexico City, and Beijing have large areas.
The perimeter-to-area ratio of metropolitan areas tends to be inversely propor-
tional to city population size. Seventy percent of the metro areas have a length-
to-width ratio <2; only Iquitos at 5.8 is very long and narrow.
In effect a broad cross-section of geography, climate, land use and culture is
represented in this set of 38 urban regions. The next two chapters will examine
these regions in some depth to discover valuable patterns and principles.