Joe Biden triumphed over Donald Trump in the presidential election in large part by reversing a feat accomplished by Trump in 2016: Biden won a much larger share of votes in America's suburbs than Hillary Clinton did four years ago. Clearly suburbs have become the new electoral battleground in national politics, and both presidential candidates made explicit appeals to their voters.

With all that political attention, you'd think we'd have arrived at a generally accepted definition of "the suburbs" — a way to distinguish them from their neighboring central cities and from the exurbs out on the metropolitan fringe. But defining what constitutes a suburb remains as elusive as ever.

I guess the simple answer is like what U.S. Supreme Court Justice Potter Stewart said about obscenity in a 1964 case: "I know it when I see it." We each have our own notions of what a suburban area is; it's in the eye of the beholder. Mostly it involves a very strong single-family-home orientation, a separation of residential, commercial and other land uses, and a heavy reliance on the automobile. Sometimes it's restricted to post-World War II construction, even if areas built earlier meet the same criteria (as some do).

It can get even more complicated. There are many neighborhoods that are primarily single-family, a result of separated land uses, and auto-reliant but that are firmly within a core city's limits. Many of the Sun Belt's largest metro areas (Charlotte, Atlanta, Houston, Phoenix and Las Vegas, for example) would be overwhelmingly suburban by that definition. However, if we consider "urban" as the antithesis of that suburban definition — a diverse mix of housing types, a mix of land uses, and greater integration and reliance on public transit — there are communities that are beyond core city limits that meet that standard (such as Cambridge and Somerville, Mass., Arlington, Va., and Oak Park, Ill.).

What we need is a baseline understanding of what constitutes a suburb. If we can't define it satisfactorily by characteristics, could we at least describe it by the numbers? I think I have one way.

Using the American Community Survey's 2019 one-year estimates, I gathered data for the nation's 53 largest metro areas, all of the Metropolitan Statistical Areas (MSAs) with more than one million residents. Then, using each metro's urbanized area and core city data, I came up with a simple, data-driven definition of city, suburb and exurb:

  • "City" simply equals core city-limits population (twin cities, such as Minneapolis/St. Paul and Tampa/St. Petersburg, are combined).
  • "Suburbs" equal MSA population minus city and exurbs population.
  • "Exurbs" equal MSA population minus city and suburbs population.

For these definitions I'm using generally accepted terms that are data-based. Core cities have definable city limits. Beyond that, however, the Census Bureau defines "urban areas" as contiguous census tracts with a population density greater than 1,000 people per square mile. Using this definition, suburbs becomes the space between the city limits and the edge of the urban area. Past the suburbs lie the exurbs, the semi-rural periphery that reaches out to the limit of the metro area.

Nationally, the composition of the 53 largest U.S. metros looks like this:

Cities-suburbs-sExurbs table  

Using this definition, you'll see that, cumulatively, "suburbs" make up nearly three-fifths of metro area population. Incidentally, that's pretty close to what Indeed.com economist Jed Kolko found when he surveyed residents on their perceptions of their living area.

Here are the city/suburb/exurb population percentage totals for the 53 largest metros:

Metro areas table  

There are some distinctions that can be found using this definition: Some core cities, such as San Antonio, Louisville, Jacksonville and Tucson, dominate the population of their metro areas. These are often cities that have pursued an aggressive annexation policy or a city/county merger — they've in effect brought their suburbs within their boundaries. On the other hand are core cities that comprise a far smaller portion of the metro area population, like Miami, Atlanta, St. Louis and Washington, D.C. In these cases, city boundaries were set early on and remain unchanged (St. Louis and Washington), or suburban incorporation proliferated at virtually the same time as city growth (Miami and Atlanta).

I admit it's not precise, and it leaves a lot of nuance on the table. But I'm willing to trade urban-like suburbs for suburban-like city neighborhoods nationwide and call it a wash. What's most important is coming up with a way to describe and evaluate the principal way Americans live. A perfect definition is likely to continue to be elusive, but it seems like getting the numbers down is a good start.