City rankings are flighty things. Lots of people try to assess what makes the “best” city, and the results often say more about the ideals of the assessor than they do of the city itself.

But despite the different criteria and measures used there are some consistencies – the same names seem to appear again and again towards the top of each table, just in different orders.

One consistent pattern is that, when it comes to assessing the global influence of particular cities, there’s a broad consensus that the United States is home to more notable cities than any other country. Urbanist Richard Florida recently distilled various lists to create a ranking of the top 25 economically influential cities around the globe. Of those, six were in the US, far more than in any other country. The list included not just the powerhouses of New York, LA and Chicago but also Boston, San Francisco and Washington.

Some of those cities automatically come to mind when you think of big American cities – but Boston? San Francisco? Are these really among the biggest cities in the US?

A city’s size is surprisingly difficult to define: all too often, the answers depend on what you mean, and what criteria you’re using.

The most frequently cited statistics out there are also perhaps the most misleading: the official population measures from that city’s local authority. The problem here is that there are no shared rules about how local government is set up. Some cities have a single governing body; others are broken up into smaller councils. Many US municipalities are also conflated with their counties, which can range in size anywhere from 20 to 20,000 square miles.

For the sake of completeness, though, here are the ten biggest US municipalities. It dates from 2007, and appears to be the most recent dataset available – even if it were up to date, though, we’d still advise you to take it with a large pinch of salt.

1) New York City (8,104,079)

2) Los Angeles City (3,845,541)

3) Chicago City (2,862,244)

4) Houston City (2,012,626)

5) Philadelphia City (1,470,151)

6) Phoenix City (1,418,041)

7) San Diego City (1,263,756)

8) San Antonio City (1,236,249)

9) Dallas City (1,210,393)

10) San Jose City (904,522)

To get a meaningful measure of a city’s size, we need to ignore arbitrary administrative borders.

Every year a St Louis based planning consultancy called Demographia publishes something rather good: the World Urban Areas Report, a sort of bumper book of city population stats. You can check out the 11th edition here. It seems to be the most complete source for this kind of thing, so perhaps we can use that to find out which cities are largest.

Demographia’s definition of city limits is defined by the “urban area… the urban footprint – the lighted area that can be observed from an airplane (or satellite) on a clear night”.  On this definition, the city ends when all the built-up suburbs and concrete run out and you get to fields. Thinking in these terms, New York City actually extends well into New Jersey and Connecticut, while Chicago straddles the borders of Illinois, Indiana and Wisconsin.

We’ve charted the biggest US cities by this measure:

Source: Demographia World Urban Atlas, 2015.

(You can see the stats below.)

There is another way of defining cities – by metropolitan area, which this means thinking of a city in terms of its labour market. All those people commuting in and out of the city each day are included within its population measure, and the places where they live, too, are incorporated into the city’s geographical boundaries.

This, too, means that the “city” spraws across administrative boundaries, not only into surrounding suburbs but into rural areas too. As one might expect, measures of a city’s size and population by this definition are invariably significantly greater than official measures.

Here are how things look on these terms:

Source: 2010 census data (the most recent dataset available).

(Again, the fall stats are below.)

This top ten is similar to the last one, but with a couple of significant differences. It is notable that, when measured in terms of their commuting labour market, the majority of cities have a slightly higher population, but the two biggest on the list do not – both New York and Los Angeles drop by a million or so.

One possible reason for this is that they both border other urban centres of varying sizes. That means that the continuous urban buildup could be larger than the functioning economic area of the city – people may be able to resist the draw of the Big Apple, if it means a shorter commute to another city within its local area. While smaller cities have satellite suburbs, these megalopolises have satellite cities which draw employment in their own right.

So what does all this mean?

It is clear that by any measure New York, Los Angeles and Chicago are the biggest cities in the US. But things are much less clear when listing a top ten. The networked mass of cities in California and Texas means that they are sometimes defined as single entities, and at other times treated as completely separate entities.

It is a messy business: as we said at the start of this thing, trying to define a city’s size depends completely on the criteria you use.

The largest urban areas in the United States:

1) New York (20,630,000)

2) Los Angeles (15,058,000)

3) Chicago (9,156,000)

4) Dallas-Fort Worth (6,174,000)

5) San Francisco-Jose (5,929,000)

6) Houston (5,764,000)

7) Miami (5,764,000)

8) Philadelphia (5,570,000)

9) Atlanta (5,015,000)

10) Washington (4,889,000)

The largest metropolitan areas in the United States:

1) New York (19,069,796)

2) Los Angeles (12,828,837)

3) Chicago (9,461,105)

4) Dallas-Fort Worth (6,426,214)

5) Philadelphia (5,965,343)

6) Houston (5,920,416)

7) Washington (5,582,170)

8) Miami (5,564,635)

9) Atlanta (5,268,860)

10) Boston (4,552,402)

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