Wednesday, June 5, 2013

Daytime Population Makes its Triumphant Return

By Matt DeVeau, Project Associate.

The U.S. Census Bureau recently released a new batch of data that I came across via a post on The Atlantic Cities titled: “The Most Important Population Statistic That Hardly Ever Gets Talked About.” Sure, that’s a click-bait headline, but I must say I agree. The statistic in question commuter-adjusted population estimates – otherwise known as “daytime population.” The reason it doesn’t get brought up much is because the most recent national data on the topic came from the 2000 Census. 

That changed recently when the Census Bureau released new commuter-adjusted population data based on 5-year American Community Survey 5-year data from 2006 to 2010. The ACS asked respondents about their place of work and residence, which the Census Bureau used to calculate daytime population estimates.

This data opens up a range of possibilities to explore, but I’ll limit myself to three quick thoughts. 

First, this is why you don’t kill the American Community Survey. Like, seriously. 

Second, as Emily Badger of The Atlantic Cities points out, this macro-look at how populations move throughout the day provides important context to discussions about regional transportation infrastructure investments. This is by no means a substitute for more sophisticated transportation modeling efforts, but data like this can help frame the issue in an easily understandable way. 

Finally, I decided to take a quick dive into the data to revisit a post of mine from earlier this year related to a Brookings Institution report on job decentralization. To quickly recap, the study analyzed how far away jobs were from the central business district of the nation’s 100 largest metro areas. Atlanta, home of Market Street, was essentially the most “decentralized” job market, according to Brookings. In my post, I noted that much of the growth on the periphery of the region was driven by retail and health care – two population-sensitive sectors – while the jobs near the region’s core tended to be higher paying. 

So what does the daytime population data say about the metro Atlanta? Of the 28 counties in the Atlanta-Sandy Springs-Marietta Metropolitan Statistical Area only one has a daytime population that grows as a result of commuting. That county is Fulton – the region’s center that is home to most of the City of Atlanta. Fulton County has a resident population of 886,982 according to the ACS data. But during the day, its population swells to 1,256,406 as a result of commuting – a 41.6 percent increase. All other counties in the metro area experienced a daytime population decline due to commuting. This trend was pronounced in counties such as Cherokee (-20.4 percent) and Paulding (-28.4) that have a lot of people but few jobs, but even counties with large economies such as Cobb, DeKalb, and Gwinnett saw single-digit percentage declines in their daytime populations. 

The ACS also provided an employment-to-residence ratio that measures the total number of workers working in an area to the total number of workers living in the area – rough indication of a county’s jobs-workers balance. Of all sub-state-level jurisdictions in the United States with at least 50,000 residents, only two had a ratio higher than Fulton’s mark of 1.86 – Washington, D.C. and Manhattan. As a percentage of the region as a whole, Fulton has 17.3 percent of metro Atlanta’s people but 32.6 percent of its jobs. 

This is not to say that Fulton’s status as a commuting magnet negates anything in the Brookings report. Counties in Georgia tend to be small, but because of its unique shape, many Fulton employment centers such as Sandy Springs and Alpharetta are further than 10 miles from downtown Atlanta. And certainly, the region is a sprawling place in all senses of the word. But more and more, I’m thinking that Atlanta’s decentralized job market is primarily a product of where people live as opposed to some sort of polycentrism that differs radically from other American metro areas.