New Area- and Population-Based Geographic Crosswalks for U.S. Counties and Congressional Districts, 1790-2020

A common problem in historical research involves harmonizing geographic units across time or different levels of aggregation. One approach is to use " crosswalks" that associate factors located within one geographic unit to different " reference" units based on relative areas . We develop an alternative approach based on relative population , accounting for heterogeneities in urbanization within counties. We construct population-based crosswalks for 1790 through 2020, which map county-level data across U.S. Censuses as well as from counties to congressional districts. Using official Census data for congressional districts, we show that population-based weights outperform area-based ones in terms of similarity to official data