Mapping Ideology of US Congress Members in the 21st Century (2000-2018)

Ezequiel Contreras

Introduction

DW-NOMINATE Scores are measures of legislators’ ideological positions in a basic space developed by Keith T. Poole and Howard Rosenthal. The proximity of two legislators in this space reflects the similarity of their voting records. The model assumes individual legislators have stable ideological positions over their congressional careers. As such, the distribution of the scores can be seen as a representation of polarization. The scores go along two dimensions. The primary dimension, which is the focus of this project, is the “left-right” dimension (sometimes called the “liberal-conservative” dimension). This single dimension correctly predicts the vast majority of legislators’ votes cast in modern Congresses in the United States. The scores for each dimension range from -1 (more ideologically left) to 1 (more ideologicaly right). The measures can be used to gauge at polarization, but comprehension of these scores can not be complete without knowledge of the historical context the votes take place in.

This project uses ideological data accessible through voteview.com. Voteview.com hosts DW-Nominate Score data for all Members of Congress from the 1st to 116th Congresses.

File Table

• map-master.qgz ….. latest master QGIS map project
• /district_boundaries_shapefiles ….. district and state boundary shapefiles
• /QGIS-Files ….. QGIS map export templates
• /member_ideology_data ….. Ideological data for House, Senate, POTUS
• /RScripts ….. mainly subset data scripts
• /qgis2web_maps ….. rough webmaps (.zip)
• /maps_png ….. rough map outputs (.png)
• /district_boundaries_shapefiles/documentation_jefflewis_ucla ….. documentation for district shapefile metadata

Rough Map Samples

• Representative NOMINATE Dimension 1 scores by Congressional District, 116th Congress (2019-2021)

• Representative NOMINATE Dimension 1 scores by Congressional District, 115th Congress (2017-2019)

• Representative NOMINATE Dimension 1 scores by Congressional District, 114th Congress (2015-2017)

• Representative NOMINATE Dimension 1 scores by Congressional District, 113th Congress (2013-2015)

• Representative NOMINATE Dimension 1 scores by Congressional District, 112th Congress (2011-2013)

• Representative NOMINATE Dimension 1 scores by Congressional District, 111th Congress (2009-2011)

• Representative NOMINATE Dimension 1 scores by Congressional District, 110th Congress (2007-2009)

• California Representative NOMINATE Dimension 1 scores by Congressional District, 112th Congress (2011-2013); district labels are readable when zoomed in.

To Do Next

• Finish color Mapping Dimension 1 Nominate Score for 116th - 111th Congresses
• add 109th congress house map layer
• add PRESIDENT nominate dimension1 score data~~
• build initial webmap
• package webmap(s) into .zip files for download

Sources

Ideological data from:

• Lewis, Jeffrey B., Keith Poole, Howard Rosenthal, Adam Boche, Aaron Rudkin, and Luke Sonnet (2020). Voteview: Congressional Roll-Call Votes Database. https://voteview.com/

Congressional District cartographic boundary data for 114th Congress and earlier from:

• Jeffrey B. Lewis, Brandon DeVine, Lincoln Pitcher, and Kenneth C. Martis. (2013) Digital Boundary Definitions of U.S. Congressional Districts, 1789-2012. Retrieved from http://cdmaps.polisci.ucla.edu on October 5, 2020

Congressional District cartographic boundary data for 113-116th Congress from:

• US Census Bureau - US Congressional District Cartographic Boundary shapefiles - Shapefiles https://www.census.gov/geographies/mapping-files/time-series/geo/carto-boundary-file.html