Image Processing Reference
In-Depth Information
The City as an Ecosystem
To establish a foundation for the V-I-S model we must first establish that the
urbanized area and its surroundings, referred to herein as the urban/peri-urban
environment, as an ecosystem, in the same sense that any portion of the earth
surface, natural and/or human may be considered an ecosystem. The peri-
urban area may be thought of as the urban fringe where a dynamic transition is
converting pre-urban land to a built environment, while the area beyond is tied to
the city through a demand for resources and other activities (Chapters 2 and 3
in this volume, also see Douglas 1983 ; Dorney and McLellan 1984 ; Quattrochi
1996 ; UNFPA 2001 ).
As in any ecosystem, energy and moisture flux are the primary drivers
in environmental dynamics. In the case of urban ecosystems, human-based
technologies impose significant influence on the energy/moisture balance
through such factors as anthropogenic energy, impervious surfaces, and various
structures (Ridd and Hipple 2006 ). Cities are perhaps the most dramatic
expressions of the transformation of natural environments by the hand of
humans. Yet, in primitive societies the degree of transformation is minimal and
the character of the settlement is quite different from that of highly urbanized
places. As settlements grow from early beginnings into villages, towns, cities, and
metropoli, the environmental nature of the settlement becomes more complex
as technology advances. The reach outward for resources expands as does the
problem of disposition of effluent. Remote sensing technology is increasingly
capable of monitoring the consequent environmental transformation. Through
remote sensing the V-I-S model provides a means of documentation of the
imperative and changing nature of human settlements worldwide (Ridd 1995 ).
The V-I-S Model
The V-I-S model suggests that the great variety of urban land cover types can be
grouped into the three general categories - vegetation, impervious surface, and soil -
plus water. These four cover types exhibit highly contrasting influences on the two
most important factors in an ecosystem: energy and moisture flux. Variations within
each category can be recognized as well by identifying sub-categories of vegeta-
tion, impervious surface, soil, and water.
In the context of the model, V stands for green vegetation, I includes surface
pavement as well as impervious roofs or elevated parking
structures, and S represents exposed soil. Graphically, the
three are presented as a ternary diagram, where the sum of
all three components is equal to 100% as shown in Fig. 6.1 .
Water is handled independently. Shadowing cast by vertical
the V-I-S model
plays directly in
the urban/peri-
urban ecosystem
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