A Method to Construct Geographical Crosswalks with an Application to US Counties Since 1790

Empirical researchers often have to map data provided for a "reporting" spatial unit, say counties in 1900, to a "reference" one, say, counties in 2010. We discuss a general method to create such crosswalks: computing the share of the area of each reporting unit nested in a given reference unit. Using these shares, data can be re-aggregated from the reporting to the reference units. We apply the method to construct a crosswalk for US county-level data since 1790 to present-day counties or commuting zones. We also provide the code to generate other crosswalks given maps of reporting and reference units.Institutional subscribers to the NBER working paper series, and residents of developing countries may download this paper without additional charge at "http://www.nber.org/papers/w26770"