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
remained unassociated to the other cities (both r2> 0.1, p>0.05).
Due to the compositional nature of a STURLA cell where the relative
proportions of all elements sum to one Figure 2 shows provides an
example 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 low-rise
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 low-rise buildings (1-3 stories).