Nature in urban regions
Bucharest, Edmonton, Iquitos [Peru], Moscow, Bangkok). The remaining 20 cities
were selected to provide a balanced set of urban regions that accomplished the
primary and secondary criteria listed (Table 5.1).
Determining urban-region and metro-area boundaries
Amajor city, as well as its boundaries, normally cannot be seen on a
satellite or other aerial image. Instead, a large mass of built area stands out, often
relatively compact, but sometimes diffusely grading into greenspace (unbuilt
area) at its edge. The city is inside the large built area, typically with the city
center centrally located. This large central clearly visible object, the essentially
continuous built area, is herein called themetropolitan areaor simplymetro area
(see Figure1.1). In general, its boundary is easily determined and marked on
thelarge images. In spots one of two mapping decisions has to be made. How
wide does a strip of greenspace need to be to exclude a peripheral built area as
aseparate suburb or town, or to cut off a greenspace wedge projecting into the
metro area? A greenspace width of 1 km (0.6 mi) was used as a general guideline.
The other mapping decision related to low-density housing development, mainly
an issue around portions of US cities. The general guideline cutoff used was a
large group of 2 ha (5 acre) house lots; areas with smaller house lots were
considered built and larger lots unbuilt.
More interesting and significant to this book is how to determine theurban-
region boundary.Arguably the central importance of an urban region relates to
interactions -- flows and movements -- back and forth between the city and its
surroundings. In this sense the urban region is a functional region. One can ask
and learn, ‘‘How does it work? What are the types, directions, and intensities of
interactions?” Delineating the urban-region boundary thus simply requires an
estimate of the intensity of flows and movements along radial lines extending
out from the city center. The boundary is where inward and outward interactions
noticeably decrease.
Numerous attributes affect movements and flows inward and outward, and
data on as many as possible were mapped on the large aerial images. Several
attributes initially thought to be important turned out not to be so, because
they usually did not extend very far beyond the metropolitan area (ends of com-
muter rail lines, communities with substantial commuter populations, airports,
sewage-treatment facilities, solid-waste disposal sites, reduced air-quality areas).
Rivers and highways hardly ever delineated urban-region boundaries. Wetlands
were too scarce around urban regions to be important determinants.
In contrast, mountain ranges often delineated urban-region boundaries.
Major political/administrative borders often determined boundaries of a region.
Another nearby major city (>250 000 population) with its own urban region