Pop SPI Den SPI ImpS SPI DMSP SPI
SPI, therefore, measures spatial scattering patterns of four different morphological characteristics – 2000 total population scattering spatial pattern index (Pop SPI), 2000 population density scattering spatial pattern index (Den SPI), 2001 impervious land cover scattering spatial pattern index (ImpS SPI), and 2000 nighttime light emissions scattering spatial pattern index (DMSP SPI).
The SPI values can be interpreted as follows: each morphological feature (i.e., 2000 total population, 2000 population density, 2001 impervious land cover, and 2000 nighttime light emissions) is evenly distributed within a megaregion when an SPI value approaches 0; each morphological feature density is extremely high in fewer areas within a megaregion when a value of the SPI approaches 1. The SPI value can be interpreted as a relative term in comparison with other SPI values because of the lack of thresholds to determine the absolute extent of spatial scattering based on a single value.
Observations of spatial scattering patterns, therefore, are conducted in terms of each morphological characteristic for the 11 U.S. megaregions and each megaregion for morphological characteristics.
As observations in terms of each morphological characteristic show, the 2000 total population spatial scattering indicates that the Southern California megaregion has the highest Pop SPI at around 0.87 and the Arizona Sun Corridor megaregion has the second highest Pop SPI at around 0.85. This means that populations in the megaregions in 2000 were extremely concentrated in fewer areas. For spatial scattering of the 2000 population density, the Arizona Sun Corridor megaregion shows the highest Den SPI at around 0.97. Northern and Southern California and Cascadia megaregions show the
second highest Den SPI, at approximately 0.94. It means for the megaregions that land consumption per capita was extremely concentrated in fewer areas in 2000. For the spatial scattering of the 2001 impervious land cover, the Front Range and Arizona Sun Corridor megaregions show the highest value of SPI at around 0.77 and 0.76 respectively. It means that megaregions with urbanized built environments represented by impervious land cover were extremely concentrated in fewer areas in the year 2001.
For the spatial scattering of the 2000 nighttime light emissions, the Arizona Sun Corridor and Front Range megaregions showed the highest SPI value at around 0.93 and 0.92 respectively. It means that in the megaregions urbanized social activities, which are represented by nighttime light emissions, were extremely concentrated in fewer areas in 2000.
The above results show that morphological characteristics observed in this study have a distinct spatial scattering pattern from each other for the 11 U.S. megaregions.
Among the morphological characteristics, spatial scattering patterns identified by 2000 population density represent the most extreme spatial concentration in fewer areas at around the 0.93 mean of the 11 U.S. megaregions Den SPIs. The spatial scattering patterns identified by 2000 nighttime light emissions also show an extreme spatial concentration in fewer areas at about the 0.85 mean of the 11 U.S. megaregions DMSP SPIs. The spatial scattering patterns of the 2000 total population demonstrate relatively low spatial concentration in fewer areas at about the 0.73 mean of the 11 U.S.
megaregions Pop SPIs. Spatial scattering patterns of 2001 impervious land cover
represent the lowest degree of spatial concentration in fewer areas at about the 0.64 mean of 11 the U.S. megaregions ImpS SPIs.
In terms of each megaregion, the 11 U.S. megaregions have the greatest deviation in the 2000 total population and the smallest deviation in 2000 population density.
Observations also show the greatest deviation of SPIs in the Northeast megaregion and the smallest deviation of SPIs in the Southern California megaregion. Spatial scattering of morphological characteristics represents such a general pattern as the highest SPI at 2000 population density, the second highest SPI at 2000 nighttime light emissions, the third highest SPI at 2000 total population, and the lowest SPI at 2001 impervious land cover. The Piedmont Atlantic megaregion represents a lower Pop SPI than the ImpS SPI, even though every other megaregion has a higher Pop SPI than the ImpS SPI. The Southern California megaregion is also exceptional in that the Pop SPI is the same as the DMSP SPI, contrasted to other megaregions were the Pop SPI is smaller than the DMSP SPI.
The overall observations for spatial scattering patterns show that such morphological characteristics of the 11 U.S. megaregions as population, density, impervious land cover, and nighttime light emissions are distributed unevenly in fewer areas. It means that megaregion scale urban structures and human habitat spatially converge in fewer areas. It is difficult to say, however, that the 11 U.S. megaregions share common patterns of spatial scattering of morphological characteristics based on inconsistencies in the Piedmont Atlantic and Southern California megaregions. It does not mean that the spatial distribution of morphological characteristics is a random
scattering of the 11 U.S. megaregions, but that spatial distribution is inconsistently concentrated in fewer areas according to morphological characteristics. The spatial scattering pattern index, however, has no power to determine whether the concentrated spatial distribution in fewer areas is clustered or not.
1.3. Spatial clustering pattern index
The results of calculations for the spatial clustering pattern index (CPI) are given in Figure 10. The CPI was calculated using the 2000 total population, 2000 population density, 2001 impervious land cover, and 2000 nighttime light emissions. The CPI, therefore, has measured spatial clustering patterns of four different morphological characteristics which are the 2000 total population spatial clustering pattern index (Pop CPI), 2000 population density spatial clustering pattern index (Den CPI), 2001 impervious land cover spatial clustering pattern index (ImpS CPI), and 2000 nighttime light emissions spatial clustering pattern index (DMSP CPI).
The CPI values can be interpreted to demonstrate that each morphological feature (i.e., 2000 total population, 2000 population density, 2001 impervious land cover, and 2000 nighttime light emissions) is randomly distributed within a megaregion when the value of CPI approaches 0, and that each morphological feature is closely clustered in subareas within a megaregion when the value of CPI approaches 1. A value of the CPI can be interpreted as a relative term in comparison with other values of CPI because of the lack of thresholds to determine the absolute extent of spatial clustering for a single value. Observations of spatial clustering patterns, therefore, are conducted in terms of
77 Close to -1 (negative one) – Chessboard pattern
Close to 0 (zero) – Random scattering
Close to 1 (positive one) – High density subareas are closely clustered
NE TT GL PA FL GC FR ASC NC SC CC
Figure 10 Calculation results of spatial clustering pattern index
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