US’ superstar cities ain’t like before

The first big data release from the 2020 Census in August contained some positive news about America’s biggest cities. The biggest of them, New York, turned out to have hundreds of thousands more people than the annual population estimates made by the Census Bureau had projected. Not one of the country’s 10 largest cities lost population between 2010 and 2020, the first time that’s happened since the 1940s. All of them now have more than a million residents for the first time ever.
The top-10’s share of the US population did shrink, as it has with every Census since 1930. But the decline — to 7.87% in 2020 from 7.94% of the population in 2010 — was the smallest since then.
Attaching meaning to this statistic is a little complicated. Big-city borders are arbitrary, with some encompassing vast areas, including what most of us would describe as suburbia, and others much more constricted. Four of the 10 biggest US metropolitan areas (Washington, Miami, Atlanta and Boston) aren’t represented in the top 10 cities list. City borders can also change over time, although the biggest such changes affecting top-10 cities occurred long, long ago with the consolidations of Philadelphia in 1854 (the “other urban places” in the chart headline refers to the formerly unincorporated Philadelphia suburbs of Northern Liberties, Southwark and Spring Garden, which all ranked among the 10 largest one or more times from 1800 to 1850) and New York in 1898 (Brooklyn had been the country’s fourth-largest city in 1890).
Membership in the top 10 can change as well; one key reason why the downward trend flattened out in recent decades is that perennial population losers Baltimore, Cleveland, Detroit and St Louis fell off the list.
Then again, the boundaries of metropolitan areas — the main alternative to cities in rankings like this — are changing all the time. The White House Office of Management and Budget adjusts them every couple of years to reflect shifts in commuting patterns and
occasionally redefines their very meaning. These changes usually add territory to metro areas but sometimes break them apart, as happened in 2003 when new OMB definitions split the San Francisco-Oakland-San Jose metro area, at the time the nation’s fifth-largest, into six different areas, none in the top 10, and the Washington-Baltimore area, then the fourth largest, into three.
Not coincidentally, the share of US population accounted for by the 10 biggest metro areas fell from 31.5% in the 2000 Census to 26.1% in 2010. It was 26.4% in 2020.
The Census Bureau also divides the US into urban and rural areas, with
the urban share of the nation’s population increasing steadily over time, to 80.7% as of 2010 (the 2020 numbers aren’t out yet). But its definition of urban casts an awfully wide net, including every settlement of 2,500 people or more, and is subject to change from time to time (the 2,500 is about to be upped to 10,000, for
example).
All of which is a long way of saying that while the population of the 10 largest cities is a flawed measure of urbanisation in the US, all the other measures are flawed too — and the top-10-city total, available all the way back to 1790, conveys some useful pieces of information. One is that, as already mentioned, the 2010s were not a decade of urban decline. The 10 biggest cities added 1.6 million residents, the third biggest such gain since 1930.

—Bloomberg