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The Census data utilized for developing the Community Layer used 2010 TIGER/Line shapefile datasets (TIGER = Topologically Integrated Geographic Encoding and Referencing). TIGER/Line shapefiles are available for free download from the US Census Bureau and include various legal and statistical geographic areas for which the Census tabulates data. The shapefiles are designed to be used in a GIS environment, with the ability to directly link the geographic areas to Census data via a unique GEOID number.
The following TIGER/Line datasets should be used:
- Counties and Equivalent Entities –primary legal divisions within each state (counties, parishes, etc)
- County Subdivisions –includes both legal areas (Minor Civil Divisions or MCDs) and various statistical areas
- Places –includes both legal areas (Incorporated Places) and statistical areas (Census Designated Places or CDPs)
- Blocks –the smallest geographical area for which Census population counts are recorded; blocks never cross boundaries of any entity for which the Census Bureau tabulates data, including counties, county subdivisions, places, and American Indian, Alaska Native, and Native Hawaiian (AIANNH) areas
- American Indian, Alaska Native, and Native Hawaiian (AIANNH) Areas
Extracting and Formatting CIS Data
A key component of the community layer is the ability to link CIS information spatially. Data from CIS cannot directly be joined with Census data. The two datasets have community name discrepancies which impede an exact match. Therefore, CIS data needs to be formatted to match Census community names. A custom report can be obtained from CIS to include a CID number, Community Name, County, State, Community Status, and Tribal status for all CIS records. Make sure all CID numbers are six digits and you follow the CIS community naming convention outlined in Table 4.2.1.1 in the Community Layer Update Technical Guide 20131206. Converting the CIS name“ADDISON, VILLAGE OF” to “ADDISON TOWN”involves removing unneeded spaces, comma, and preposition to make the join successful to the Census data. Using a comprehensive report at a national level gains efficiencies as bulk edits can be made. Data for each state should be extracted as needed by separating the CIS data into each type of community corresponding to the Census geography layers used, and a new JoinID column (e.g. ADDISON TOWN) can be created for each dataset allowing the CIS data to be joined to the Census data.
Creating Incorporated Place Boundaries, Assigning CID
The creation of the Jurisdictional Boundaries layer should occur on a state-by-state basis, so that individual differences associated with each state’s legal boundaries can be addressed more easily. For each state, the first step involves selecting and exporting all Incorporated Places from the Census Places data layer, so that only legal areas such as cities, towns, and villages are included. Within this incorporated places layer, the existing NAMELSAD10 field contains the geographic area’s name and the legal description/type, for example “Addison town”for the Town of Addison. Add a new JoinID field to the layer to convert the NAMELSAD10 field to uppercase characters. This JoinID field will then match the format of the extracted CIS data and allow for the best possible join results, since discrepancies in capitalization would otherwise prevent records from joining. Add new blank fields for CID, CIS_NAME, and CIS_COMMENTS to store CIS attributes.
Now join the CIS data to the incorporated places layer using the JoinID fields. The added CIS fields can be bulk calculated for all matching records. For each state, if any incorporated places with duplicate names exist within the CIS data, the CIS fields must be manually calculated.For example, in the state of Ohio, there are two entries for “OAKWOOD VILLAGE”, one is located in Paulding County, and one is located in Cuyahoga County. Since the Census Place data can cross county boundaries and the county(ies) are not stored as attributes, the Census Place layer will need to be loaded into a GIS map along with the county boundaries to visually determine the county each “OAKWOOD VILLAGE”polygon is located within.The correct CIS data should be manually calculated for these polygons.
Any unmatched records in the CIS data should be manually checked to determine if there are discrepancies in spelling or formatting between the Census data and the CIS data (e.g. Sweetwater versus Sweet Water, or St. Florian versus Saint Florian). Add a temporary field to the CIS data containing the name as shown in the Census data; this allows the CIS data to be rejoined to the incorporated places layer when needed.
For some CIS records unable to be matched to the Census incorporated place data, the Census Designated Places (CDP) statistical geographical areas can be utilized (e.g., special areas such as air force bases or fire districts in Connecticut, or communities that became incorporated after the most recent Census Places layer was created). For CIS communities that exist within the CDPs, copy the polygon into the working incorporated places layer. Add new blank fields for CID, CIS_NAME, and CIS_COMMENTS to the dataset. Now, join the data and calculate the attributes for the new blank fields. All remaining unmatched CID records need to be reported in the Unassigned CID Table within the database.
For all polygons derived from the 2010 Census Places layer, the “SOURCE”field in the Jurisdictional Boundaries layer ispopulated with the code “P”.
Creating County Subdivision Boundaries, Assigning CID
For certain states such as Michigan, there are townships or other county subdivision areas of legal authority that have CIDs or may potentially be assigned CIDs in the future (i.e. at least one other similar county subdivision currently has a CID assigned to it in the state). Boundaries for these areas can be created by extracting the applicable Minor Civil Divisions from the Census County Subdivision dataset. To keep the Jurisdictional Boundaries layer topologically correct, delete the incorporated places within each county subdivision using the ArcGIS Erase function.
Within the county subdivisions layer, the existing NAMELSAD10 field contains the geographic area’s name and the legal description/type, for example “Mason township”. This field alone cannot be used as an effective join field to the CIS data since the same township name is usually used within multiple counties. To determine the county name for the subdivisions the COUNTYFP10 field containing the county’s FIPS code can be joined to a FIPS lookup table and calculated the county name within each county subdivision. Then create a new JoinID field and add it to the county subdivision layer. Perform a calculation to concatenate the NAMELSAD10 field with the new county name field. Remember to convert the text string to uppercase characters so that the JoinID format matches what was already created from the CIS data.
Similar to the join procedure described above for incorporated places, the CIS county subdivision data can then be joined to the county subdivisions so that the added CIS fields can be calculated. Add new blank fields for CID, CIS_NAME, and CIS_COMMENTS to the dataset. Now, join the data and calculate the attributes. All unmatched CID records need to be reported in the Unassigned CID Table within the database.
For all polygons derived from the 2010 Census County Subdivisions layer, the “SOURCE” field in the Jurisdictional Boundaries layer is populated with the code “S”.
Note, in the states of Minnesota, North Carolina, and North Dakota, only those townships that currently have a CID assigned to them are incorporated into the Jurisdictional Boundaries layer. This is due to the fact that these states have townships that comprise the entire extent of the counties, and these states also have CID numbers assigned to each county. In order to maintain these county CID numbers and to maintain a topologically correct layer (no overlapping polygons) all townships could not be included in the Jurisdictional Boundaries layer.
Creating County Boundaries (Unincorporated Areas), Assigning CID
After the creation of the incorporated places and county subdivisions is complete, the boundaries for the unincorporated parts of counties can be created. Using the Census Counties layer, the incorporated places and county subdivisions within each county can be deleted using the ArcGIS Analysis Tools\Overlay\Erase function. The output of the function is depicted in Figure 4.2.4.1. To start, create a new JoinID field to the layer to convert the NAMELSAD10 field to uppercase characters and add new blank fields for CID, CIS_NAME, and CIS_COMMENTS to the dataset.
Similar to the join procedure described above for incorporated places, the CIS county data can be joined to the county boundaries so that the added CIS fields can be calculated. All unmatched CID records need to be reported in the Unassigned CID Table within the database.
For all polygons derived from the 2010 Census County layer, the “SOURCE” field in the Jurisdictional Boundaries layer is populated with the code “C”.
Note, for many states that contain townships or other county subdivisions that comprise the entire extent of the counties, the county boundaries are not included in the Jurisdictional Boundaries layer, in order to maintain a layer that is topologically correct (no overlapping polygons). The townships in these states are assigned CID numbers, while the counties do not have CID numbers. This includes the states of Connecticut, Maine, Michigan, New Hampshire, New Jersey, New York, Pennsylvania, Rhode Island, and Vermont.
Assigning 2010 Census Population
For the Jurisdictional Boundaries, the 2010 Census population can be calculated by joining the layers to the corresponding Census TIGER/Line layers with Demographic Profile 1 attributes, using the GEOID10 field. When joined, the population can be directly calculated into the spatial data.
However, the population for the county subdivisions and the unincorporated areas of the counties must be calculated using Census block data, since the boundaries do not directly match any Census tabulation areas. First, convert the Census block polygon layers containing population data to centroid points, making sure to select the option to force the point to be located within the polygon. Next perform a spatial join to sum the population of all points located within each unincorporated county. This summed value is the assigned population for the county. This spatial join operation versus an area-weighting technique can be utilized since all of the boundaries used to create the Community Layer are Census boundaries that completely contain Census blocks (blocks never cross boundaries of Census tabulation areas).
The three intermediate boundary layers for incorporated places, county subdivisions, and unincorporated portions of counties for all states can be merged to create a single Jurisdictional Boundaries layer that contains both CIS and population data. In both the Jurisdictional Boundaries and Tribal Boundaries layers, to maintain a unique identifier for each polygon, add a new field called “AREA_ID” and calculate as follows:
Jurisdictional Boundaries J_AREA_ID = 2-digit State FIPS code + “J” + XXXX
The XXXX denotes a unique numerical counter within each state (e.g. 0001, 0002, 0003, etc.).