Wilnelia Rivera
UEP 232: Intro to GIS
Assignment 4: GIS Data Quality
Assessment
Project Benchmark Description
Located in the northern region of Suffolk
County Massachusetts, Chelsea,
Massachusetts is an immigrant city that is
facing rising land use challenges as the
population continues to increase (see Figure
1). A local organization, the Chelsea
Collaborative (CC), is working with local
youth leaders and the local government to
build more schools, centers for children and
youth, and recreational spaces. But before
they can make any proposal they need an
assessment of the actual inventory. This
analysis will require the location information
of child day care centers, children and youth
services, elementary and secondary schools,
land use, and parcel information. Data layers
for this analysis will include geocoded child
day care centers (NAICS code 624410),
children and youth services (NAICS code
624110), elementary and secondary schools
(NAICS code 611110), and land use
information from MASSGIS.
Figure 1, City of Chelsea all street centerlines
(Census 2010 TIGER)
Positional accuracy of street centerlines,
hydrography, and parcels is only relatively
important; an accurate, general location of
these layers is enough for CC. Land use
information by parcel type and the inventory
of centers and services must be accurate so
that CC can propose youth focused
redevelopment projects to the local City
Council while making a case for investment
by funders.
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Table I. Data Benchmarks
Roads
Hydrography
Child Day Care Centers
Children and Youth Services
Elementary and Secondary Schools
Land Use
Positional
Accuracy
Required
Attributes
+/- 10 feet
Street names
+/- 20 feet
+/- 9 feet
+/- 9 feet
Center names
Street names
Important
Important
Current
Current
School names
Commercial,
Residential, Indusrial
Commercial
Important
Important
Current
2005
+/- 9 feet
+/- 19 feet
Completeness Time
Period
Road Centerline Data: The road datasets compared include Census TIGER 2010 roads and
Chelsea street centerlines layered over aerial imagery for a location where the MASSGIS appears
especially incomplete. Overall the two data sets match and both have high positional accuracy. But
the lack of missing attributes affects the completeness of the MASSGIS data. (See Figure 2). It is
best that the CC use the census street centerlines data in terms of accuracy, completeness, availability
of street names.
Figure 2. Chelsea street centerlines dark (blue) and Census TIGER line files (red)
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Hydrography: Hydrological layers from figure three (below) shows the City’s data in light blue and
the census data in dark blue layered over aerial imagery for a location where the census data appear
especially incomplete. However, the City and Census data do not match at all. It appears that the
Census Bureau has yet to map all the necessary hydrological layers for Suffolk County. That said it is
best that CC use the MASSGIS hydrography data in terms of accuracy and completeness.
Figure 3. Census hydrography (dark blue) and City of Chelsea data (light blue)
Given the various problems that both data present it is best that the CC use the census data for
street center lines and positional accuracy while using the MASSGIS hydrology data. But the city
hydrography data does not contain the names of water features as attribute information, which
could impact the quality of map design. Since land use by parcel type is much more important than
the hydrology data for the client’s project it is not important fort the client if the city data is missing
attribute information.
Child Day Care Centers
Positional Accuracy: To assess positional accuracy, child day care centers were geocoded using two
methods: the ArcGIS North America Geocode service and Google Earth. There are only ten child
day care centers in Chelsea, and the general locations of the stores seemed accurate based on Google
Earth search. (See Figure 4.). I would recommend that use of this data set by CC.
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Figure 4 : Child day care centers locations
Both locations on Figure 4 have matching longitude (71 W) and latitude (42N).However, a few
discrepancies in the geocoded datasets were found. Generally speaking day Care centers obtained
using the North America Geocode service often ended up close to (or in the middle of) the road, as
shown in Figure 4.
Completeness: The data sets are complete based on a Google Earth search that revealed all ten child
day care centers in approximately the same location.
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Currency: The NAICS database, from which the child care centers addresses came, is only updated
every five years. In addition, the NAICS database does not capture small family child care services
that usually operate within residential parcels.
Attribute Accuracy: While the Child day care centers geocoded using the ArcGIS North America
Geocode have positional accuracy, it is difficult to confirm attribute accuracy, or that a child care
center still exists at a given address. That is why a physical confirmation by the CC is necessary of
their location. In addition, I would recommend a canvassing campaign that seeks to identify home
based child day care center.
Children and Youth Services
Positional Accuracy: To assess positional accuracy, children and youth services were geocoded using
the ArcGIS North America Geocode. There are only four centers for children and youth services in
Chelsea, and the general locations of the centers were misplaced. (See Figure 4). I would not
recommend using this data set.
Figure 5: Children and Youth Services locations and Chelsea road names in Census TIGER street
centerline files (red)
Completeness: The data sets are complete based on a Google Map search that revealed all children and
youth services approximately at the same location.
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Currency: The NAICS database, from which children and youth services addresses came, is only
updated every five years. In addition, there may be a classification error in the NAICS that limits the
definition of what is considered children and youth services, which leads to an undercount of
children and youth services.
Attribute Accuracy: While the children and youth services geocoded using the ArcGIS North America
Geocode have positional accuracy, it is difficult to confirm attribute accuracy, or that children and
youth services still exists at a given address. That is why a physical confirmation by the CC is
necessary of their location. In addition, I would recommend a canvassing campaign that seeks to
identify additional locations that provide children and youth services that did not meet NAICS
criteria.
Elementary and Secondary Schools
Positional Accuracy: To assess positional accuracy, elementary and secondary schools were geocoded
using the ArcGIS North America Geocode. There are only thirteen elementary and secondary
schools in Chelsea, and the general locations of the schools seemed to be generally misplaced. (See
Figure 6.) But the placement is relatively close to street centerline that their overall positional
accuracy is confirmed. I would recommend that use of this data set by CC.
Figure 6: Elementary and Secondary schools and Chelsea road names in Census TIGER line files
(red)
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Completeness: The data sets are complete based on a Google Map search that revealed all elementary
and secondary schools approximately at the same location.
Currency: The NAICS database, from which elementary and secondary schools addresses came is
only updated every five years.
Attribute Accuracy: While elementary and secondary schools geocoded using the ArcGIS North
America Geocode have positional accuracy, it is difficult to confirm attribute accuracy, or that
elementary and secondary schools still exists at a given address. The data set also contains the names
of the school, which will be helpful for CC’s project since not all the locations are actual elementary
and secondary schools. That is why a physical confirmation and differentiation by the CC is
necessary of their location.
Land Use
Positional Accuracy: The metadata of the MASSGIS shape file, landuse2005_POLY_suff, confirms the
positional accuracy of the parcel types. According to the metadata MASSGIS geo-referenced parcel
types with ArcGIS North America Geo code, conducted several tests with various datasets of higher
accuracy, and fieldwork to confirm positional accuracy. (See Figure 7.) I would recommend that use
of this data set by CC.
Figure 7. Chelsea land use by parcel type
Completeness: The data sets are complete up to 2005.
Currency: The MASSGIS shape file, landuse2005_POLY_suff, was last updated in 2005, which means
that CC may need to conduct additional fieldwork to complete any gaps.
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Attribute Accuracy: While the parcel types geocoded using the ArcGIS North America Geocode has
positional accuracy, it is difficult to confirm attribute accuracy, or that parcel types still exists at a
given address. Given the importance of this dataset for CC, I recommend that it confirm all open
recreation space since it will shape and influence their youth redevelopment projects.
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