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Tuesday, January 07, 2020  11:05 AM  (29)

How will the 2020 Census impact redistricting within Pennsylvania?

The next redistricting of political boundaries across the nation will be based on the data collected from the 2020 decennial census which aims to count the nation’s entire population as of April 1, 2020.     

At the end of 2020, the first data the Census will report from the 2020 decennial census will be new total population counts for all states. Congress uses this data to reapportion the number of seats in the U.S. House of Representatives. Projections by Election Data Services Inc., a political consulting firm, predict that as a result of population changes between 2010 and 2020, Pennsylvania will lose one of its current 18 congressional seats as the result of population changes this decade.

The geographic boundaries of most congressional districts must also be adjusted in a process called redistricting to ensure that all house districts within a state represent a nearly identical number of residents. Redefining congressional districts relies on data for census blocks, the smallest level of census geography.  This detailed data for redistricting will be released for individual states on a rolling basis beginning in February 2021 with data for 8-9 states made available each week until completion. The specific order of states is not yet known. As a result, the specific date for Pennsylvania data to be made public is not yet determined.

Similar redistricting also takes place every decade for all 253 districts that make up the Pennsylvania General Assembly including the 203 seats in the Pennsylvania House of Representatives and the 50 districts of the Pennsylvania State Senate.

While the data compiled in the 2020 decennial census will be the authoritative data for redistricting, the Census Bureau has produced annual estimates of the population for states and counties each year since 2010. The latest Census Bureau population estimates for counties are for 2018. These annual estimates provide a strong indication of the pattern of population change that has been taking place within Pennsylvania. By extrapolating estimated changes in population between 2010 and 2018, it is possible to project the anticipated impact of political redistricting on counties in southwestern Pennsylvania.  

The table below summarizes the population for Allegheny County, the remaining counties within the Pittsburgh Metropolitan Statistical Area (MSA) and Pennsylvania from each decennial census that has been completed since 1980.  Also shown are the latest census population estimates for 2018, and a projection of where these populations will be in 2020. 

Following the 2010 decennial census, the average population of a district in the Pennsylvania House of Representatives was 62,573.  Pennsylvania is estimated to have sustained moderate population growth since 2010. As a result the average district in the Pennsylvania House of Representatives is projected here to be 63,138 in 2020.  Allegheny County’s projected 2020 population will equal the equivalent of 19.3 state house districts, a decline from 19.6 house districts in 2010.  The loss of roughly 3/10’s of a state house district is a fraction of the decline the county experienced between 2000 and 2010, which saw the county lose the equivalent of 1.6 house districts. Proportional changes are expected for the larger state senate districts, which are roughly 4 times as large as a typical district in the Pennsylvania House of Representatives. Allegheny County is projected to lose the equivalent of under 1/10th of a state senate district. 

The remaining counties within the Pittsburgh MSA (Armstrong, Beaver, Butler, Fayette, Washington, and Westmoreland) are projected to collectively lose the equivalent of 6/10ths of a district in the Pennsylvania House of Representatives. That result would mean that 2010-2020 is the first time in recent decades where the suburban counties of the Pittsburgh region lost more representation in the Pennsylvania General Assembly than did Allegheny County.

These projections are based on the results of the 2010 decennial census and the 2018 census population estimates for the state of Pennsylvania and individual counties.  The population projection for 2020 used here is a forecast that assumes the average rate of estimated population change between 2010 and 2018 for each Pennsylvania county continues through 2020. 

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