A new definition of downtowns and their live-work connections.

• Position: News & Numbers

A new report from the Center City District, a business improvement district sponsored by the private sector, examines 231 major employment centers and their adjacent residential neighborhoods in 150 of America's largest cities, defined by total number of jobs, and tracks their changes in the last decade.

The report, titled Downtown Rebirth: Documenting the Live-Work Dynamic in 21st Century U.S. Cities, provides a standard way of defining downtowns and anchor institution districts, enabling a comparison of employment and population trends in all major American cities in a way that accounts for the diverse physical shapes of major employment nodes and their adjacent residential areas.

Most of the data used to define downtown areas come from federal surveys, which do match up or present sufficient detail. For instance, in a September 2012 report, the U.S. Census Bureau attempted to quantify population change in central cities by examining trends in a two-mile radius around the city hall of the principal city in each metropolitan area. Of course, city halls are not always at the geographic center of the downtown area, and a simple circle does not capture the shapes of urban commercial areas--although it can include rivers, highways, and state lines. (The two-mile circle for the New York City downtown area, for...