Image Processing Reference
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City: largely
impervious surface
Agriculture: mix of
vegetation and bare soil
Wilderness: largely bare soil
Spectral properties of land cover
Fig. 3.1 The urban gradient may be discontinuous
be the places least habitable by humans. As the fraction of vegetation increases,
there is an implicit increase in the availability of water and where there is sufficient
water the possibility of agricultural increases and agriculture creates a signature on
the ground that is typically distinct from areas that have not been modified by
humans. However, the nature of urban places is that the built environment is dominant,
and so cities are distinctly noticeable from the air because vegetation gives way
immediately, discontinuously, to impervious surfaces.
The proportional abundance of impervious surface is the baseline measure of
urbanness, as suggested by the Ridd V-I-S model, but shade is also a factor, espe-
cially in areas dominated by tall buildings. Thus, in areas that are generally urban,
the simple addition of the impervious surface and shade fractions should provide an
appropriate measure of the proportional abundance of land cover most associated
with an urban place. In agricultural areas, where shade may indicate canopy cover
or water-saturated ground, it would be less appropriate to combine the impervious
surface with the shade fraction.
The other aspect of landscape metrics is the quantification of the spatial con-
figuration of the patches comprising each land cover class. We may know that
60% of a given area is covered by impervious surface (the measure of composi-
tion), but we would also like to know how those patches are arranged within the
area under observation. McGarigal et al. ( 2002 ) notes that configuration is much
more difficult to assess than composition and over the years a large number of
measures have been developed in an attempt to capture the essence of landscape
configuration. However, it is important to keep in mind that most measures of
landscape configuration were developed for the purpose of describing landscape
ecology and have only recently been shown to have an adaptation to the measure-
ment of the urban environment (Herold et al. 2002 ). One of the more interpretable
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