mySidewalk’s data library includes historical Census estimates, but comparing data from different Census years is not always a straightforward procedure. The boundaries for most Census geographies change over time for a variety of reasons including political redistricting, annexation, population change, and the emergence of new governmental entities.
Geographic harmonization is a statistical technique used to facilitate comparisons of Census concepts over time. For example, geographic harmonization allows us to “transpose” Census 1990 estimates from Census 1990 geographies to Census 2010 geographies.
mySidewalk supports data from the following Census products:
ACS 2007-2011 5 Year Estimates
Current 5-year ACS Estimates
Major updates to Census boundaries generally coincide with the release of decennial Census data. Since the most recent major update to Census geography boundaries occurred with the release of the 2010 Census, it was necessary to use geographic harmonization to support Census 1990 and Census 2000 data alongside other Census products in our data library.
We used Census block-level geographic crosswalks provided by the National Historical Geographic Information System to perform reapportionment of Census 1990 and Census 2000 block group level estimates to Census 2010 block group geographies. We then aggregated the the block group level data to higher levels of geography (states, cities, etc.) via weighted block-point apportionment (WBPA). For more information on how the crosswalk files were developed, see the methodology documentation provided by the NHGIS.
Steven Manson, Jonathan Schroeder, David Van Riper, and Steven Ruggles. IPUMS National Historical Geographic Information System: Version 12.0 Geographic Crosswalks. Minneapolis: University of Minnesota. 2017. https://www.nhgis.org/user-resources/geographic-crosswalks