You can tell a lot about a place by who doesn't want to be there any more. Or, conversely, by who wants to move in.
A city that seeps population over time invariably has deeper problems driving its demographic change, like poor school districts that can't keep young families, or weak job prospects for its college grads. A county that attracts new residents, on the other hand -- maybe young people in particular, or retirees -- likely has the right amenities to lure them. Maybe a certain job sector. Or golf course communities.
In this way, we can divine some of the fortunes of different corners of the country simply by watching how Americans move around over the years. Each year, about 10 million Americans relocate to a new county. Map all those moves from one Census to another, across decades, and by race and age demographics, and you can see the Great Migration of blacks from the South, white flight to northern suburbs, the hollowing out of Rust Belt cities and the rise of the Sun Belt.
Researchers at the University of Wisconsin, Michigan Technological University and the University of New Hampshire have built just such a database dating back to the 1950s. Their tool tracks net changes in population by county, all across the country, for each decade since the 50s (taking into account estimated deaths and births in between each decennial Census). The results tell hundreds of stories, but we've pulled out a few of them.
Here is a map of total net migration across the 2000s in the U.S., with orange counties losing the most people and purple counties gaining the most. The legend is shown at right.
At that largest scale, broad patterns emerge as the two coasts and much of Texas gain population at the expense of the Great Plains during the 2000s. Here is a different picture, over the same period, looking only at net migration by 15-29 year-olds (based on their age at the end of each decade):
Zoom in -- you can do this on the full interactive map here -- and it's clear that Rust Belt counties around Detroit, Cleveland and St. Louis have lost many young people, who have relocated, on balance, to places like San Diego, Austin, and Atlanta. The mapping tool also illustrates these population changes in chart form. Here, those six counties are contrasted with their migration trends by age:
The tool also illustrates some familiar historical patterns by race. In this map, from the 1970s, white populations have clearly left major Midwestern cities like Chicago, Detroit and Cleveland, with increased in-migration into surrounding counties:
Wayne County (Detroit) lost 26.6 percent of its white population in the 1970s. Cook County (Chicago) lost 15.5 percent, and Cuyahoga County (Cleveland) 20.1 percent.
A generation earlier, in the 1950s and 1960s, we can see a related chapter in history, in the broad migration of non-whites (as the Census collectively classified minorities then) out of the South and into much of the rest of the country:
Nonwhite net migration in the 1950s.
You can zoom in here for a closer take on individual communities. Each map shows a relatively simple calculation (the total population in each county at the end of a decade, relative to what it was projected to be at the beginning). But that one number, particularly when compared to other counties nearby or across the country, reflects much about what may have happened in the interim years.