Environmental Engineering Reference
In-Depth Information
FIGURE 2.4
Urban spatial growth in the Atlanta metropolitan area during different periods: high-density urban (upper) and
low-density urban (lower). The boundary for 13 counties in Atlanta is shown.
in the following years in the time series is shown. In this way,
the urban extent of six dates was summarized on one map. By
assigning a unique color to the net addition of each year on
the combined map, the progressive growth of high-density or
low-density urban land can be perceived (Fig. 2.4).
The nature of change is to analyze land conversions using
cross-tabulation or matrix analysis that assigns a unique class for
each coincidence in two input layers, thus capturing different
combinations of change. This method was used to characterize
the land conversions for different time periods. Given the total
number of land classes, there are 36 possible combinations
for each period. Because this study focused on the conversion
of forest, cropland/grassland, or cultivated/exposed land into
urban uses, only six combinations were selected for further
analysis, while the other were merged into a single unit. The
conversion coding system is shown in Table 2.5, along with
the conversion statistics for different periods.
increment) between 1987 - 1993. These additions were primarily
concentrated in several inner counties, such as Fulton, Cobb,
DeKalb, and Clayton. Significant growth took place by 1999 and
2007, with more new development areas concentrating in north-
ern and northeastern areas. The linearly concentrated pattern
became more multinucleated. The 1999 and 2007 distributions
show further enhancement of this transition as the spread took
place largely along transportation routes and around urban cen-
ters, particularly in some peripheral counties, such as Coweta,
Cherokee, Forsyth, Paulding, and Fayette. In 2007, the high-
density urban use occupied 106 860 hectares, or 10.22% of the
total land area, which was about 254.88% increase in land when
comparing to 1973. The daily increment was approximately 6
hectares or 15 acres between 1973 - 2007.
The evolution of spatial pattern of low-density urban use,
mainly residential, is clearly perceived in Fig. 2.4 (right). In 1973,
the low-density urban use occupied 76 861 hectares, or 7.35%
of the total area (Table 2.3). Although the low-density urban
land shows signs of spreading outward, its large share was clearly
concentrated in the inner city core and several inner counties.
A somewhat linear pattern can also be seen along several major
transportation routes. Thus, the spatial pattern of low-density
urban use in 1973 can be described as a form of concentration
mixed with some degree of dispersal. Significant growth occurred
in 1979 and 1987, with net addition of 52 231 and 48 665 hectares,
respectively (Table 2.4). Most of the new additions occurred
outside the central city core, concentrating in four inner counties
of DeKalb, Clayton, Fulton, and Cobb, and in three exterior
counties of Gwinnett, Rockdale, and Fayette. Growth in the
northern, northwestern, and northeastern directions was quite
2.3.5
Interpretation and analysis
BasedonFig.2.4(left),thespatialexpansionofhigh-density
urban use is clearly visible. In 1973, the high-density urban
use was small, occupying only 2.88% of the total land area
for Atlanta (Table 2.3). The outward spread is quite clear in the
1979, 1987 and 1993 patterns, following the major transportation
routes. The net addition was 8276 hectares (or 27.48% incre-
ment) between 1973 - 1979, 16 242 hectares (or 42.31% incre-
ment) between 1979 - 1987, and 13 002 hectares (or 23.80%
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