Quantifying Urban Diversity: Multiple Spatial Measures of Physical, Social, and Economic Characteristics - Computational Approaches for Urban Environments - page 150

Hillier's conclusions must be taken in context and cannot be seen as a refutation
of Jacobs' ideas about block length. Along with the limited research into the street
length - livability dynamic - there is essentially no current research available that
examines the role of building age mixes with regard to livability and diversity.
In addition to the research that has been conducted focusing on a single one of the
four generators of diversity, there have been a limited number of studies that have
attempted to include elements of at least three of the generators (again, building
age mix is absent in these studies). Miles and Song ( 2009 ) examined Portland,
Oregon, which has utilized many of Jacobs' ideas in its planning and found that
the city “has been successful in creating neighborhoods at several economic scales
that feature not only the connectivity, accessibly, mixed land use and access to public
transit that characterize 'good' neighborhoods from a physical perspective, but also
'good' social environment indicative of strong ties and collective efficacy.” This
finding echoes the earlier research of Song ( 2005 ) who examined three different
communities that have utilized “smart growth” policies and found that “only when
all these dimensions - connectivity, density, mixed land uses, accessibility, and
pedestrian walkability - are combined can they create synergy by having amenities
that complement one another.” Regarding the four generators of diversity, Jacobs
herself writes, “all four in combination are necessary to generate city diversity;
the absence of any one of the four frustrates a district's potential” ( 1992 , p. 151).
Cervero ( 2002 ) also examines multiple parameters, this time strictly from the
perspective of travel mode choice. Utilizing Traffic Analysis Zones, he found that
“drive-alone and group-ride automobile travel fell relative to transit riding as gross
densities increased at both the trip origin and destination. And land-use mixture at
both trip ends lowered the probability of driving alone or ride-sharing versus taking
a bus or train, ceteris paribus” (Cervero 2002 ). These papers all underscore the wide-
ranging impact that Jacobs' ideas about density, land use, and street networks can
have on the livability of the urban environment.
A number of researchers have emphasized the importance of scale when studying
the built environment. Tesfazghi et al. ( 2010 ) illustrated how having areas of
aggregation that are too large can mask the variability that exists at a lower level.
This reinforces the work of Openshaw and what he termed the “modifiable areal
unit problem,” noting that “the definition of these geographical objects is arbitrary
and (in theory) modifiable at choice; indeed, different researchers may well use
different sets of units” ( 1983 ). This highlights the importance of utilizing small,
yet standardized units of aggregation. Martinez ( 2009 ) chose to study quality of
life indicators at a disaggregated level stating that, “when indicators are generated
at high levels of aggregation they can give a misleading idea of the problem they
address and quantify.” Apparicio et al. ( 2008 ) who examined a mix of subjective
and objective quality of life parameters at an intra-urban level note that, “since
individuals' daily lived environment is not on a metropolitan scale, it is important to
find the appropriate scale so that the indicators can express the heterogeneity of the
conditions faced by urban residents.” The research presents a convincing argument
to carefully account for the level of detail at which a study is undertaken.