Geoscience Reference
In-Depth Information
investigator, provided the appropriate data is available. Additionally, the dwelling
location data used here may be among the most difficult to obtain for a researcher
in another city. Although such cadastral data are becoming more widely available,
that availability is not universal to be sure. In that case, the number of households
per census block could be used as a substitute. It is clear that Jacobs was concerned
with dwellings themselves, rather than households, and we know that the census
can - and not infrequently does - associate more than one household with a single
dwelling. The measures are therefore not identical; however, the difference this
substitution would create in the results is unknown, it may be small, and it may
be place dependent. A test of the effect of this substitution is an area for future
research.
The next parameter, block length, is also well represented using the method
applied here. It is noteworthy that this method is sensitive to the inclusion of limited-
access roadways, such as interstates. This is, from Jacobs' perspective, a benefit of
the methodology, as expressways and the like are viewed by Jacobs as detrimental to
the city, particularly when they form a barrier that negatively influences neighboring
communities (Jacobs
1992
, pp. 258-259). Thus, having a methodology that is
sensitive to these types of intrusions can be powerful. This is illustrated in the case
study presented here, by the lower ranking that is given to the Georgetown area, due
to the presence of the Whitehurst Freeway. The presence of the Southeast-Southwest
Freeway in the Southern quadrants of the city also plays a significant role in the
outcomes in those locations with regard to the block length parameter. It is noted
that the block length processing was quite computationally intensive. In the future it
may be appropriate to investigate other surrogates for block length, such as number
of intersections per unit area.
The third parameter, mix of building age, is also well quantified using the
methodology presented here. Perhaps the most challenging aspect of this parameter
is that, given few enough structures, it can become excessively sensitive to the range
of building ages. Thus, in the case study, the area of the National Mall performed
very well, due to the low number of structures within this area. However, the casual
observer may disagree with this assessment, particularly given the large geographic
area that this particular block group includes. Thus, in terms of the spatial mixing of
building ages, the National Mall performs poorly, since buildings of differing ages
are not necessarily in close proximity to one another. This is perhaps the parameter
of Jacobs that is most open to interpretation, since Jacobs provides little guidance
for what range of ages (20 years? 50? 100?) is most beneficial to the district in
question. In the future, the exploration of an entropy or diversity index to measure
lack of diversity among the building ages may prove fruitful, particularly if a spatial
parameter can be included.
The fourth parameter, mixed-primary uses, is the most complex of the four
parameters to calculate. However, the method presented here may represent an
improvement over other methods that have been utilized in the past. This method
provides the level of “mixedness,” rather than simply presenting a binary variable, or
counting the number of different uses within an area, ignoring their actual proximity
to one another within that area. The results of the calculation appear to provide
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