Mapping Inequality

Tim Holland, a graduate student in Geography at McGill, working with Andy Gonzalez and Greg Mikkelson, and I has recently mapped out US household inequality (using the Gini coefficent to measure inequality) at a county level for 1970, 1980, and 1990. The inequality data is from François Nielsen at University of North Carolina – Chapel Hill.

The striking increase in USA inequality between 1970 and 1990 primarily occured in the 1980s. The spatial pattern of inequality is interesting, but perhaps unsurprising. Why inequality decreased in some counties in the central USA is perhaps more interesting.
USA inequality by county 1990

US inequality by county 1970

USA inequality by county change 1970-1990

For comparison, below is a map of international inequality from Wikipedia (note the color scheme is slightly different).
International Inequalityglobal inequality index

2 thoughts on “Mapping Inequality”

  1. I was curoius how the Gini Index calculated for each county; What unit of analysis was used : individuals, families, blocks, tracts, or cities?

    Thanks you for putting this information on the web. This is informative and nicely presented.

    Does the census count illegal, new immigrants?

    It seems that many of the most ‘unequal’ counties are rural, where I conjecture live small populations, with native american and new immigrant populations.


  2. In the maps Gini is calculated for household income.
    The census counts people at residences regardless of their status.

    US states vary a lot in their levels of inequality, with the South being more unequal than the Northeast or Midwest.

    More information on the census can be found on the US census’s site.

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