July 2006

Resident Population, 2000

People usually think of population in terms of residents, that is, the number of people living in an area. That number can change significantly during the day, however, because some people commute to work in an area different from that in which they live. The measure of daytime population captures this by adjusting resident population by the number of in-commuters and out-commuters.

Daytime Population Change

The populations of counties such as Franklin (which contains Columbus), Hamilton (Cincinnati), Cuyahoga (Cleveland), Allegheny (Pittsburgh), and Fayette (Lexington) all expanded at least 5% during the day in 2000 because more workers commuted into than out of them. Not surprisingly, the daytime population of surrounding counties tended to fall. For example, the number in Campbell County, which borders Cincinnati’s Hamilton County, fell an estimated 18% during the day.

Employment to Residence Ratio

Very similar to the daytime population measure is the employment-to-residence ratio, which represents the number of people working in an area relative to the number of workers living there. A ratio higher than one would indicate that more workers are working in an area than living there, making the area a net importer of labor. This is the case in most counties that contain major cities.

City Populations, 2000

Among the largest cities in the District, Pittsburgh’s population changes most by day, expanding more than 40%. Indeed, the number of workers who have jobs in the city is almost double the number who live there.