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. 1 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) 2 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. 3 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. 4 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. 5 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) 6 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. 7 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. 8