CASA professor Mike Batty recently asked me to crunch some historical population data for British population centres. The starting point was some census-based data going back to 1901 that have been adjusted1 to the local authority boundaries for 1991 to make them comparative across a period of significant change to census boundaries. These I reworked a bit by grouping urban authorities together to encompass the wider hinterland areas of 63 leading cities (more detail below) so the figures would broadly reflect the growth of Britain’s urban populations. Plotting the resulting figures offers some interesting insights into the trends of growth and decline in Britain over the last century or so. Firstly a plot of the actual data, with population on a log scale as it spans many orders of magnitude. The cities are coloured by rank in 1901 so those with highest relative growth/decline become more visible:

growth_comb_plot_full

In my opinion this is useful for reading the data, but is noisy and not so easy to decipher. So I also did a rank plot, showing only relative population growth and decline (at the expense of absolute trends):

rank_plot

It’s suddenly much easier to see which cities gained most (e.g. Reading, Bournmouth, Southend) and which lost out (e.g. Blackburn, Dundee) over the 20th century, in a relative sense. Some care should be taken with interpretation – for example it’s possible for a city to e.g. rise strongly through the rankings by starting in the low-centre of the distribution, exceeding mean growth rate2, and finishing in the high-centre (e.g. Southampton).

There is a broad discernible trend of higher growth cities in the southeast of England and up the Thames valley while many in the north and Midlands have declined, reflecting a broad shift of the nation’s economic centre of gravity towards London. It is also worth noting that most of the rank activity is in the middle group of cities where the populations levels are more equivalent. Glasgow and Liverpool both show significant population decline in the past five decades, but their rankings are largely unchanged because they remain high in absolute terms.

Primary Urban Areas

To define the urban hinterlands of these cities, I used Primary Urban Areas (PUAs), a system of definitions of leading urban boundaries established for England by the Department for Communities and Local Government, and extended by the Centre for Cities think-tank, who defined some additional zones to expand the system to include leading urban centres elsewhere in the UK3. The PUAs do seem to have been designed a little arbitrarily. London’s boundaries have spilled outwards from the Greater London Authority zone to swallow up some satellite areas but not others.

London

And a comparison of Cambridge and Norwich (East Anglian towns of equivalent population – on the same scale below) shows a much more restrictive zone for the former, despite it having lots of high-tech research industry in the surrounding rural area, whereas Norwich’s ‘urban’ zone extends to include much of The Broads..

Cambridge_Norwich_PUAs

Some other shortcomings are detailed in their wikipedia page4. But nevertheless these PUAs are selected here for data aggregation for their semi-official status and relative compatibility with the historical population data.

Notes:

  1. This work was originally undertaken by Helen Mounsey (Dept. of Geography, Durham University) as part of her 1982 PhD thesis, “The cartography of time-changing phenomena: the animated map”. I appended the data for 2011 by point-over-polygon overlay of Output Area data points over PUA boundaries and then aggregating. Any discrepancies for 2011 can probably be attributed to diverging methods (York seems an example). Anyone interested in how the PUAs overlay the 1991 local authority boundaries can check out this map.
  2. Across the island the population grew on average by approaching 50% from 1901 to 2011, and this same rate was also reflected by the mean of just the urban populations.
  3. Northern Ireland’s are omitted here as it is missing from the population data.
  4. Most of the reference links on the page are now dead so the origins of these criticisms of the PUAs are unclear, but they seem fair. One is of “multiple distinct settlements.. being treated as if they were a single city” (e.g. Birmingham/Wolverhampton), while another concerns the significant interactions between some PUAs, such as the flows of workers commuting between them (e.g. Manchester/Bolton/Wigan).
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