Results
The most prevalent composite class in Philadelphia contains trees,
grass, paved surfaces, and low rise buildings (‘tgpl’) (Table 1). The
‘tgpl’ class accounts for about 57% of total city area and can be found
in all parts of the city and was largely homogenous in spatial
distribution (Figure 1A). The second largest class, ‘tgplm’ at 8.5% of
the area, which is similar to ‘tgpl’ except it includes midrise
buildings, is concentrated in the center of the city and along a few
main corridors to the North and West. STURLA classes were able to
identify the role of urban structure influencing ST (Figure 1B). Classes
generally hosted ST that were unique (Figure 1B) and significantly
different (Table 2) compared to all other classes with the exception of
‘tgbp’ with similar ST values to ‘tgwp’ and ‘tgwpl’.
The prevalence and distribution of the STURLA classes in Philadelphia
differs from what we found in previous studies of urban structure NYC
and Berlin (Figure 2). In Berlin and NYC, ~1/3 of the
landscape can be explained by one highly composite STURLA class. Another
difference between the results in Philadelphia and previous studies is
the number of classes that cumulatively explain 90% of the area of the
city. Ten classes covered 90% of the area of Philadelphia while the
same number of classes only covered 79% of the area of New York City
and 68% of the area in Berlin. Despite these differences, pairwise
comparison of each city revealed that STURLA class proportions were not
significantly different between the cities (all p>0.05)
Still, Berlin and NYC were highly correlated
(r2=0.952, p<0.05) while Philadelphia’s
distribution of urban structure remained uncorrelated to the other
cities (p>0.05).
Due to the compositional nature of a STURLA cell where the relative
proportions of all elements sum to one Figure 2 provides an example of
compositional variability within the most common class in Philadelphia
‘tgpl’ using six grid cells taken from a larger city-wide random sample.
The different grid cells and corresponding satellite imagery show the
different types of buildings and proportion of each element of the
class, trees, grass, paved surfaces, and lowrise buildings, can vary
greatly from one another but still fall into the class. Most grid cells
from the ‘tgpl’ class show row houses or single-family detached houses
since they fall within the size parameters of lowrise buildings (1-3
stories).