Tori Okner
Friday, Oct 19, 2012
UEP 232
Assignment Four
GIS Data Quality Assessment: Food Access in North Dorchester (JFK – Columbia Point - Savin Hill)
Project Description
In a corner of North Dorchester, the neighborhoods around JFK, Columbia Point, and Savin Hill blend
into one another and create the rich diversity found at the fringe of cities. Part of the traditional Polish
Triangle leads into an area now known as Little Vietnam. UMass Boston is across the area’s center
transit routs and abuts the quickly gentrifying Savin Hill (formerly known as Stab & Kill). To some old
timers, the evolving demographics are an affront to the entrenched culture of the neighborhood. To
some of the new urban pioneers, change is not coming fast enough.
This area has been chosen for a food access assessment both for its long history as an underserviced
neighborhood and its potential for development. Four data layers have been selected to assess current
retail food options, land use zoned for commercial space, open space in the neighborhood to consider
the potential for outdoor markets, and area nursing and rest homes which may serve as centers for food
distribution.
Positional Accuracy
At this initial stage of the project, relative positional accuracy will suffice for most data layers. The
principal goal of the assessment is to visualize the distribution of existing and potential food access
points with the long-term objective of ensuring an easy, affordable, and equitable access across the
neighborhoods.
Standard Data Layers
Exactness of road centerlines and hydrography is unnecessary at this nascent stage. In a comparison of
two data sources, the first from Census TIGER 2010 and the second from MassGIS (updated in 2012),
very little difference was found at the neighborhood level. Where inaccuracies appeared, they were
similar in both data sets. In figure 1, the Tiger 2010 data shows a centerline far to the right. The line is
also pulled off center in figure 2, with data from Census TIGER 2010. However, when measured the
centerline in question, in figure one, is 33.2 feet from the left curb and only 13.2 feet from the right.
This discrepancy is less extreme in figure 2, where it is 18.4 feet from the left and 13.2 from the right.
Figure 1
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Tori Okner
Friday, Oct 19, 2012
UEP 232
Assignment Four
Figure 2
Hydrography
There is a clear distinction between the two-hydrography layers used to illustrate the coast that
delineates the eastern boundary of this area. Note that figure 3, with data from MassGIS, covers more
area than figure 4, culled from Census TIGER 2010 Area Water source. Still, this difference is not relevant
for the project at hand.
The HYDRO 25K POLY from the MassGIS data is at the scale of 1:25,000 and was last updated in
2011. According to the metadata, the layer is, “a hybrid of data based on USGS Digital Line
Graphs (DLGs), scanned mylar separates obtained from the USGS, and digitized hydrographic
features from paper USGS 1:25,000 Topographic Quadrangle maps. This layer had previously
contained features from the USGS 1:100,000 hydrography; these have been replaced with
features from the scanned mylars.” As a general rule, the more features, the greater the error.
Here though, the MassGIS data seems more accurate than the TIGER 2010 Area Water source.
Figure 3
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Tori Okner
Friday, Oct 19, 2012
UEP 232
Assignment Four
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Tori Okner
Friday, Oct 19, 2012
UEP 232
Assignment Four
Figure 4
Project Specific Data Layers
Grocery Stores
To begin the food access assessment, it is important to know what resources exist for food retail in the
neighborhood and where they are located. All area grocery stores listed with the North American
Industry Classification System (NAICS) were included. The list of store addresses was geocoded using
two different methods. The first uses an Address Locator tool through the North American Geocode
Service. The second relies on latitude and longitude and in this instance, was significantly more accurate
than the first. In figure 5, all of the neighborhood grocery stores have been condensed into a single
point, which was positioned in the center of North Dorchester. Apparently, the North American
Geocode Service does not have sufficient geographic information for Dorchester and defaulted to place
each business in the center of the area. In figure 6, each of the grocery stores appears as a distinct point.
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Tori Okner
Friday, Oct 19, 2012
UEP 232
Assignment Four
Figure 5
Figure 6
Still, in figure 7, the limitations of the latitude and longitude is visible. Though the majority of the sites
seem to be correct, there are sites listed as markets that no longer exist despite the fact that the data
set is from 2012 (according to Reference USA which provided the NAICS information). Below, the
neighborhood Shaws is correctly identified but a vacant parking spot is also marked as the site of a
store.
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Tori Okner
Friday, Oct 19, 2012
UEP 232
Assignment Four
Figure 7
Land Use
The Boston Redevelopment Authority provides information on land use categories. Both commercial
and industrial zoning may allow for future development of food retail, processing, and potential growing
space. Although the data below does not reflect current usage and/or vacancy, it is still useful in proving
a general sense of where development may occur. In figures 8 and 9, red indicates zoning for
commercial space (commercial, mixed residential commercial, and commercial land) and purple is
industrial.
Figure 8
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Tori Okner
Friday, Oct 19, 2012
UEP 232
Assignment Four
The land use data is additionally limited because it does not include details on which parcels have
received variances or distinctions allocated by the planning board. In figure 9 for example, a building is
zoned for industrial use but has been converted into a 60-unit residential condo building.
Figure 9
Open Space
Open space, a designation given to undeveloped land, or areas of water, or land set aside for
preservation, may be used for future farmers markets, mobile food vendors, or other means of
temporary distribution. While largely accurate, the open space data layer provided by the Boston
Redevelopment Authority is not 100% complete for these neighborhoods. There is no date provided so
it is unclear whether the time period is the reason for the incompleteness. In figure 10, a large,
neighborhood park held by a non-profit trust, is not marked as open space; neither is a smaller green
space in the neighborhood. Figure 11 provides a closer view of the park.
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Tori Okner
Friday, Oct 19, 2012
UEP 232
Assignment Four
Figure 10
Figure 11
Nursing Homes / Rest Homes
Nursing homes, rest homes, and other communal spaces provide additional sites for food distribution
from mobile food sources, or drop off services such as the Brown Bag program provided by the Greater
Boston Food Bank. The metadata on nursing and rest homes includes the source for the data layer: the
Division of Health Care Quality within the Massachusetts Department of Public Health with an update in
2007. This data layer exemplifies the opportunity for error at various scales. In figure 12, six area
nursing and rest homes are visible. This data is shown at a 1:24,000 scale which, according to the
US National Map Accuracy Standards, should be accurate within +/- 40 feet.
Figure 12
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Tori Okner
Friday, Oct 19, 2012
UEP 232
Assignment Four
Figure 13 captures a smaller portion of the same area, at a scale of 1:20,000. It includes another facility,
calling into question the completeness of the data as shown at 1:24,000. Note the addition of the Cusing
Manor Community Support Facility at the top of figure 13.
Figure 13
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