Mapping to Visualize Inequality
Dr. Andrew Taylor, a professor of Political Science in the School of Public and International Affairs at NC State University, is writing a book provisionally titled, "Our Equitable Democracy: American Politics and Economic Outcomes in an Age of Inequality." He contacted Data & Visualization Librarian Jeff Essic in May 2019 for assistance creating 16 maps, which will illustrate the effects of income inequality in politics.
Overview
Dr. Taylor compiled his data into a spreadsheet with values for each US congressional district for the 98th (1983-1985), 103rd (1993-1995), 108th (2003-2005), and 113th (2013-2015) Congress. The values represented (1) Gini coefficient by household, (2) the household median income, (3) the proportion of households in the highest income cohort, and (4) the proportion of households in the lowest income cohort. The highest and lowest income cohorts vary across decades and are defined by Census data.
Dr. Taylor needed to create US Congressional district maps for each Congress showing the data within five breakout classes for each of the four data categories. One challenge was that Alaska and Hawaii needed to be shown adjacent to the Continental US map in a way that was not facilitated by the available Congressional District GIS data. Also, the final maps needed to be exported as high resolution grayscale for publication.
How We Did It
The Congressional District shapefiles were downloaded from a UCLA website, http://cdmaps.polisci.ucla.edu/. Two Esri Desktop GIS software applications — ArcMap and ArcGIS Pro — were then used to create the maps. To make modified shapefiles with Alaska and Hawaii adjacent to the Continental US, ArcMap was used to convert polygons of those states from shapefile "features" to "graphics" (an option not available in ArcGIS Pro). The graphics were moved and placed West of Texas, and then re-converted to features. For all four Congresses, the entire state of Alaska has been just one district and Hawaii has had two districts, so the same district features could be used for all the maps.
Next Dr. Taylor's spreadsheet data had to be joined to the Congressional District shapefiles. For successful joins, there needed to be an ID field in his spreadsheet identical to the ID fields in the Congressional District shapefiles. By sorting both of the datasets by State, Congress, and Congressional District, the ID columns in the shapefiles were copied and pasted into his spreadsheet for perfect data joining.
Finally, for making the maps, ArcGIS Pro was used which offers the advantage of being able to work with multiple maps and layouts within one project file. Thus, once the first layout template was built, it was easily duplicated and the symbology field changed to generate the remaining 15 maps and export them to PDF.
