Geography notes: The fundamental unit of geography used in this analysis is the census tract, which approximates a neighborhood. All tract data have been compiled to conform to 2010 Census tract boundaries. To find a tract based on street address, visit the Census Bureau geocoding website.

Primary cities are defined here as the first named city in the official metropolitan statistical area title, as well as any other city in the metro area title that has a population of 100,000 or more. A census tract is assigned to a primary city if its centroid, or center point, falls within the boundary of the primary city. Otherwise it is assigned to the suburban portion of the metro area for purposes of aggregation.

Defining "nearby" jobs: The number of "nearby" jobs for a given census tract (i.e. neighborhood) represents the number of jobs that are within a typical commute distance from the center point of that tract. Typical commute distances are based on the median commute distance in each metro area. Commute distances are measured between workers' origin and destination tracts "as the crow flies" (i.e. Euclidean distance).

Creating aggregate measures: Tract-level data are aggregated to create statistics for larger geographic areas like metropolitan areas, primary cities, or the nation as a whole. Aggregate figures represent the average number of "nearby" jobs for all tracts in the relevant area, weighted by tract population. Aggregate figures may also be thought of as the average number of jobs near the typical resident.

Sources: Authors' analysis of U.S. Census Bureau data; specifically, the 2000 and 2012 ZIP Business Patterns, the 2011 Longitudinal Employer-Household Dynamics (LEHD), Census 2000 (from the Geolytics Neighborhood Change Database), and the 2009-2013 American Community Survey.

Necessary employment data are not available for the state of Massachusetts, so metropolitan areas in that state are excluded from this analysis.