Better Maps with Census Centers of Population

Jonathan Schroeder, IPUMS Research Scientist, NHGIS Project Manager

The best mapping resource no one’s using?

In the domain of U.S. population mapping, the Census Bureau’s centers of population may be the nation’s most underused data resource. Before I explain why, let’s cover some basics…

What are they? A center of population represents the mean location of residence for an area’s population, roughly the average latitude and longitude, adjusting for the curvature of the earth. For the last three decennial censuses (2000, 2010, 2020), the Census Bureau has published centers of population separately for U.S. states, counties, census tracts, and block groups.

Where can you get them? Through the Census Bureau website, you can download files containing the latitude and longitude coordinates for centers of population. To facilitate mapping and analysis, IPUMS NHGIS has transformed the coordinates into point shapefiles, available for download through the NHGIS Data Finder.

What are they used for? At the moment, not much! But there are dozens of settings where they’d be helpful. I’m hoping this blog will help get the word out, and if it does, you might now be reading this in some future age, marveling how we ever went so long without using them!

OK, how should we use them? In the case of statistical maps—my focus here—centers of population are wonderfully effective for placing proportional symbols. I share lots of examples down below to demonstrate, but first, let’s consider the general advantages of proportional symbol maps compared to a more common alternative: choropleth maps…

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IPUMS Announces 2020 Research Award Recipients

IPUMS research awardsIPUMS is excited to announce the winners of its annual IPUMS Research Awards. These awards honor the best-published research and nominated graduate student papers from 2020 that used IPUMS data to advance or deepen our understanding of social and demographic processes.

IPUMS, developed by and housed at the University of Minnesota, is the world’s largest individual-level population database, providing harmonized data on people in the U.S. and around the world to researchers at no cost.

There are six award categories, and each is tied to the following IPUMS projects:

  • IPUMS USA, providing data from the U.S. decennial censuses, the American Community Survey, and IPUMS CPS from 1850 to the present.
  • IPUMS International, providing harmonized data contributed by more than 100 international statistical office partners; it currently includes information on 500 million people in more than 200 censuses from around the world, from 1960 forward.
  • IPUMS Health Surveys, which makes available the U.S. National Health Interview Survey (NHIS) and the Medical Expenditure Panel Survey (MEPS).
  • IPUMS Spatial, covering IPUMS NHGIS and IPUMS Terra. NHGIS includes GIS boundary files from 1790 to the present; Terra provides data on population and the environment from 1960 to the present.
  • IPUMS Global Health: providing harmonized data from the Demographic and Health Surveys and the Performance Monitoring and Accountability surveys, for low and middle-income countries from the 1980s to the present.
  • IPUMS Time Use, providing time diary data from the U.S. and around the world from 1965 to the present.

Over 2,500 publications based on IPUMS data appeared in journals, magazines, and newspapers worldwide last year. From these publications and from nominated graduate student papers, the award committees selected the 2020 honorees.

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Mapping Block-Level Segregation: The Twin Cities’ Black Population, 1980-2010

Research, data preparation, story and graphics by Amalea Jubara and Yaxuan Zhang (Minnesota Population Center, Summer Diversity Fellows), mentored by Jonathan Schroeder (IPUMS Research Scientist) and Ying Song (Assistant Professor, Department of Geography, Environment & Society)

Edited by Jonathan Schroeder (IPUMS Research Scientist)

IPUMS NHGIS Block Data: An Expanding Collection

The most spatially precise U.S. census data are block-level tables, summarizing population and housing characteristics for millions of blocks throughout the country. IPUMS NHGIS provides block-level tables for the 1970 to 2010 decennial censuses as well as block boundary files for 1990, 2000 and 2010. This collection is set to grow substantially in the next few years as NHGIS adds new 2020 census block data and as we continue with a major initiative to construct 1980 and 1970 block boundary files. This expansion will open up new possibilities for high-precision spatial analysis across a longer time span.

A Case Study of the Twin Cities’ Black Population

To demonstrate some of the potential value of this expanding collection, we use NHGIS block data, including some not-yet-released 1980 block boundaries, to explore the recent history of racial segregation and integration in the Black population of the Twin Cities of Minneapolis and St. Paul, Minnesota, from 1980 to 2010. We present the block data in an interactive map along with data on early-20th-century racial covenants and the “redlining” zones of the Home Owners’ Loan Corporation (HOLC), recently published by the Mapping Prejudice and Mapping Inequality projects.

The block-level changes since 1980 show a striking trend toward greater dispersion and integration of Black residents, but segregation persists; several neighborhoods still have uniformly low or high proportions of Black residents. By overlaying racial covenants and HOLC zones with the block data, we can also find cases where the historical discriminatory practices appear to have left a lasting imprint on the distribution of Black residents.

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