New York Metropolitan ACS Geodatabase (NYMAG): User Guide
This guide provides basic instructions on how to create thematic maps using NYMAG in ArcGIS. The NYMAG was created to accommodate socio-economic and demographic analysis of New York City (5 boroughs) and the New York metropolitan area using census divisions called Public Use Microdata Areas (PUMAs). For a detailed explanation of the geodatabase's components and construction, consult the metadata on the download page.. To learn about Census ACS data, consult the ACS website.
PUMA land areas, boundaries, and points are included in the geodatabase for creating thematic maps of the census data tables. A number of other geographic areas are provided for reference. A full listing of feature classes is below. Feature classes that contain the word "boundaries" represent legal boundaries, while the other features represent land areas suitable for thematic mapping. Please consult the data dictionary for a full listing of ACS data tables.
| Feature Class | Description |
|---|---|
| ne_boundaries_2008 | State boundaries for northeastern states |
| NY_NJ_PA_metro_statisitcal_area | Combined statistical area polygon (New York metro area) |
| nyc_counties_2008 | County land area for New York City. Hyrdological features erased |
| nyc_counties_boundaries_2008 | County boundaries for New York's 5 boroughs. Area includes hydrological features. |
| nyc_pumas_2008 | PUMA land areas for New York City. Hydrological features erased. |
| nyc_pumas_boundaries_2008 | PUMAs for NYC's 5 boroughs. Area includes hydrological features. |
| nyc_pumas_points | Point feature class to allow for easy mapping of margin of error columns. |
| nyc_facilities | Airports and other large installations for reference. |
| nyc_greenspace | Large parks, wildlife areas, and cemeteries for reference. |
| metro_area_places_2008 | Place land areas for the NYC Metro Area. Hydrological features erased. |
| metro_area_places_boundaries_2008 | Place boundaries for NYC metro area. Area includes hydrological features. |
| metro_area_pumas_2008 | PUMA land areas for the NYC metro area. Hydrological features erased |
| metro_area_pumas_boundaries_2008 | PUMA boundaries for the NYC metro area. Area includes hydrological features. |
| metro_area_pumas_points | Point feature class to allow for easy mapping of margin of error columns. |
All feature classes are projected in the geographic coordinate system NAD83.
Using NYMAG
The geodatabase contains PUMA summary level data tables which can be joined to boundary files using the GEO_ID2 column within the Census ACS 3 year estimate data tables and the PUMA5ID00 column found within the PUMA feature classes.
All columns within NYMAG tables are labeled with a field number provided by the Census. In order to locate tables and fields by their codes, a data dictionary and a summary dictionary of common variables is provided within the .zip file. To join a data table to a PUMA feature class, first find the variables you are interested in by consulting the data dictionary. Next, locate the table and column number for the variable of interest.
By opening the geodatabase in MS Access, you will see each table is named using the census code. For instance, table B01001 corresponds to “Sex by Age” and B11016 corresponds to “Household type by size”. Use the data dictionary to locate the data you are interested in analyzing.
Image 1: Data Dictionary. Tables are listed under their Census code and description in the data dictionary. Table codes correspond to those within the geodatabase. See below.
Image 2: MS Access. Tables are easily located using MS Access.
Image 3: MS Access. Locate the column you wish to analyze by viewing the ACS data tables in MS Access. Here, we have chosen the total median household income in 2007 inflation-adjusted dollars in table code B19013. Note: You may also peruse data using ArcCatalog.
Once you have located the appropriate table, you can select a column corresponding to the specific variable of interest. For instance, within table B19013, Median Household Income, you might be interested in representing the total Median Household Income in column B19013_1_EST as shown in the image above.
Each variable has both an estimate and a margin of error. Estimate column names end with “_EST” while margin of error column names end with “_MOE”.
After determining which variable(s) you need, open ArcCatalog and connect to the New_York_Metro_Geodatabase.mdb. Next, launch ArcMap from the toolbar in ArcCatalog.
Launch ArcMap and add your geography and an ACS Census table. In this case this will be a feature class representing PUMAs for the New York Metro area, metro_area_pumas_2008 and the table representing Median Household Income, B19013.
Image 4: ArcMap. Add your geography features and data tables to ArcMap.
Now, right-click on your geography, scroll down to “Joins and Relates” then select “Join ”.
Image 5: ArcMap. Open Joins dialog in ArcMap.
On the join data screen, choose the ”PUMA5ID00“ field as the field that you want to base the join. Then select the appropriate census data table you wish to join to the feature class, and choose the GEO_ID2 field as the data table joining field.
Image 6: ArcMap. Open Joins dialog in ArcMap. Selecting the correct join columns in the census data table and feature class.
Once the tables are joined, you can open the attribute table for the boundary layer; you will see all of the attribute data for the layer, plus all of the data from the census data table. By opening the properties of the boundary file and selecting the symbology tab, you may select how your variables are represented in the map. More on this below.
Margin of Error
In order to map margin of error columns, simply repeat the process using the feature class titled “metro_area_pumas_points ”. To add a Census data table, join it to the feature class using the same columns referred to above (PUMA5ID00 for the feature class and GEO_ID2 for the census data field). Once the join is complete, choose which margin of error column you wish to represent by right clicking on the points feature class in the arc map table of contents, select “properties”, in the left table of contents select “Quantities”. Under the fields header there is a pull down menu titled “Value”. From the pull-down, select the margin of error column you wish to represent. You may then adjust number of classes, classification and color from the layer properties window.
Image 7: ArcMap. Selecting representation of Margin of Error in ArcMap.
Customizing Data
In some cases you may want or need to modify the data tables to better suit your purposes. For example, the census breaks data on age down into five-year cohorts by gender. If you wanted to map all persons (male and female) of a particular age group, you would have to modify the data by creating a new field that combines men and women for each age group. This can be accomplished either in ArcMap (by adding a new field in ArcCatalog, and then going into the edit mode in ArcMap and populating that field using a calculation) or in Microsoft Access by creating a query, creating an expression that will create a new calculated field, saving the query as a make-table query, and running the query to create a new table with the new field.