1.3.10b Exploitation of the contextual indices
In order to
illustrate the potential and the complementarity, but also the redundancy of
contextual indices presented in this Unit, let us apply to the description of
the spatial arrangement of land cover types in an urban area. Figure 3.6
presents the spatial distribution of 5 categories of land cover
(Forest/bush, Meadow, Building, Road, Pavement) in an urban area made up
of 4 distinct zones: individual housing, collective habitat,
industrial park and green area. The size of the cells is of approximately
15m on side. These thematic properties being categories,
they correspond to a nominal level of measurement.
Urban area made up of 5 different zones
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The description of the spatial arrangement of thematic properties
of these units of observation (cells) can begin with the identification of the
most represented land cover category in the neighborhood. We will thus choose
to retain the modal value in the moving window. In order to experiment the effect
of the neighborhood size on this index of majority
(central tendency), we will choose a window size of 3x3 as well as 5x5.
Modal property of the neighborhood in windows of size 3x3 and 5x5
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One can observe on figure 3.7 the prevalence of the meadow category
for the 2 zones of habitat, of the forest/bush type for the green area and of
the pavement category for the industrial park. When a window of larger size (5x5)
is applied, then the spatial smoothing is more marked, thus reducing the presence
of vaster regions (objects) such as the buildings of big size in the industrial
park and in the collective habitat.
Indices of texture for windows of size 3x3 and 5x5
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