The latest instalment of our weekly series, in which we use the Centre for Cities’ data tools to crunch some of the numbers on Britain’s cities. This week we’re getting a bit wonkish.

Back in September, we published a massively geeky piece looking at various ways of defining Britain’s cities, and ranking them in a list.

We concluded that, while there was no definitive way of ranking them you could come up with a sort of typology, to get a sense of which league cities were playing in. It looked like this:

  • Megacity (c10m people): London
  • Second cities (c2m people): Birmingham, Manchester
  • Major cities (c1m people): Glasgow, Leeds, Liverpool, Newcastle, Sheffield
  • Large cities (c500,000-800,000 people): Belfast, Bristol, Nottingham, Southampton/Portsmouth, Leicester, etc.

It was a fun post, for a certain value of fun – but it’s now out of date. One of the definitions we looked at was the one favoured by the Centre for Cities, which in turn had got it from the Department for communities & Local Government. That’s the “primary urban areas”: collections of local authorities that function a bit like single cities.

The problem is that, last December, the CfC updated its PUAs. Some – like Swansea and Bournemouth – grew, to incorporate new areas. Others – Liverpool, Glasgow, Reading – lost councils and shrank. London did both, while a council reorganisation means that Belfast’s boundaries bare almost no relation to the previous incarnation. A few cities disappeared from the list altogether, while others appeared from nowhere.

None of this actually matters to how cities function on the ground – but since you, dear reader, enjoy arguments about boundaries and love lists as we do, we thought it worth showing what it’d done to the rankings.

Here’s the top 10 British cities by population, under the old PUA rankings. The figures are for 2013:

  • 1. London – 9,750,500
  • 2. Birmingham – 2,453,700
  • 3. Manchester – 1,903,100
  • 4. Glasgow – 1,057,600
  • 5. Newcastle – 837,500
  • 6. Sheffield – 818,800
  • 7. Liverpool – 793,100
  • 8. Leeds – 761,500
  • 9. Bristol – 706,600
  • 10. Belfast – 675,600

And here’s the top 10 under the new ones. (Still 2013, to keep the figures comparable.) 

  • 1. London – 9617300
  • 2. Birmingham – 2453700
  • 3. Manchester – 2395300
  • 4. Glasgow – 967800
  • 5. Newcastle – 837500
  • 6. Sheffield – 818800
  • 7. Leeds – 761500
  • 8. Bristol – 706600
  • 9. Nottingham – 650100
  • 10. Liverpool – 616900

Liverpool has dropped from 8th to 10th place. Belfast, previously 10th, has dropped out of the list altogether (it’s now all the way down at 16th). Its place in the top 10 has been taken by Nottingham, which previously ranked 11th. 

There are other changes that haven’t affected the rankings, too. Manchester has grown quite substantially, thanks to its conquest of Bolton and Rochdale. Glasgow has shrunk.

In all, of the 60 cities included in both the old and new sets of PUAs, 12 of them have seen boundary changes. Here they are, ranked by the percentage change in their populations.

Newport and Swansea have both increased in scale quite considerably – the former from around 150,000 to around 240,000; the latter from 240,000 to around 380,000. Tiny Crawley, meanwhile, has shrunk by more than half, from 250,000 to 110,000.

When I started writing this, I didn’t really expect to have any conclusion, in particular: I just thought it’d be a fun piece for the demographic stats nerds. (Hi, guys!) But, to my surprise, I’ve got one.

As you’d expect, the most extreme percentage changes have been seen in smaller cities, where the loss or gain of a single local authority can have a substantial impact on city size. But there are two exceptions. Liverpool’s population in the new rankings has dropped by 22 per cent. That’s the result of the defection of St. Helen’s which, in turn, seems likely to reflect the rise of neighbouring Warrington as a local economic power. As Warrington has risen, more people in Liverpool’s eastern suburbs have commuted east, rather than west, and St Helen’s is no longer obviously just a dormitory zone for Liverpool.

The population of Manchester, meanwhile, is 26 per cent bigger in the new rankings – thanks to its incorporation of Bolton and Rochdale. That probably reflects its growing importance as an economic centre for a large chunk of the north west.

We shouldn’t read too much into this. It’s just one way of defining a city. Nonetheless – the changes to PUAs do look a little like they might reflect Liverpool and Manchester’s relative fortunes.

Here’s an interactive map showing the population’s of Britain’s cities under the new PUA definitions: hover over a city to get the data. Enjoy.