206 Urbanization models and the regions
Based on considerable landscape ecology and other literature, numerous spe-
cific ecological characteristics were known to correlate with these broad spatial
attributes. Therefore the limited number of broad spatial attributes served as
convenient informative indices or surrogates for groups of detailed ecological
characteristics.
Forcomparing and evaluating alternative urbanization patterns, this two-
tiered approach, using broad spatial attributes as indicators of detailed ecologi-
cal characteristics, appears promising. However, in the case of urbanization the
attributes chosen must effectively measure effects on two key dimensions, nat-
ural systems and their human uses.
Outward expansion of the built environment produces obvious effects in the
urban-region ring, but also some effects within the metropolitan area that war-
rant evaluation. For example, a semi-natural area in the city is enriched by
periodic arrivals of species from the countryside. If urbanization expands out-
wardin concentric zones, the semi-natural area becomes progressively more iso-
lated, less enriched by species arrivals, and more impoverished (Soule 1991 ). Also,
concentric-zone urbanization outside of green wedges is likely to simply convert
them into embedded elongated greenspace patches. That severs connection to
surrounding countryside for species, and truncates recreational opportunities
forpeople living nearby in the city. The degradation of both biodiversity and
recreational use in patches progressively more embedded in urban land is widely
illustrated: Torrey Pines in San Diego/Tijuana; Batu Caves in Kuala Lumpur; Stone
Mountain in Atlanta; Mill Creek Park in Edmonton (Saleyet al.2003,Wein2006);
desert tortoise habitat in Las Vegas (Beatley1994); and Montjuic in Barcelona
(Boada and Capdevila2000,Forman 2004a).
Finally, the area of the urban-region ring itself is relevant in evaluating urban-
ization options. Outward urbanization in small urban regions (e.g., Philadelphia)
may quickly reach the boundary of the urban region. In some cases an urban
region boundary can expand outward, but in other cases it is constrained in
place by an adjacent urban region or a high mountain range. Indeed, urbaniza-
tion from a city may affect an adjacent urban region, and vice versa.Four urbanization models
From the range of urbanization patterns and models introduced in the
previous section, and based on accumulated literature, map-and-image analyses
and personal observations, four models emerged for evaluation. These four --
(1) concentric zones; (2) satellite cities; (3) transportation corridors; and (4) dis-
persed sites -- are quite different, and may represent nearly all major global
trends in outward urbanization pattern (Figure8.2). The four core models have