The changing geography of the UK economy

The methodological briefing below sets out the results of the 2015 review of the primary urban area (PUA) definition of cities. The results of this review will be used as the base unit of analysis for Centre for Cities’ work from 2016 onward, starting with Cities Outlook 2016.

From an economic point of view, a city is the concentration of a large amount of economic activity in a relatively small area. The best performing cities make the most of this density so that the value of what they produce is greater than the value of the inputs (workers, land etc.) that they use to produce it. This process is known as agglomeration.

Given that the mission of the Centre for Cities is to look at the economies of UK cities, it is the economic concentration perspective of the city that we are most interested in. This means that we require a definition that best matches this requirement. A number of different approaches could be used. But by defining cities principally on their built-up area – that is, the physical footprint of a city – the PUA definition is, in our view, the best option.

We have worked with the academics at CURDS, University of Newcastle to update the PUA definition and refine the methodology. We did this in three main ways:

  • By using the daytime population of the city, as opposed to the resident population used previously, to better capture an economically active place
  • By increasing the threshold to 135,000 people to reflect overall population growth
  • By reducing the emphasis on travel to work areas (TTWAs) placed on the original definition, as these are less significant for determining an urban, economically active core.

This has lead to the following changes in the list of cities we analyse:

  • Based on this revised and refined approach to defining PUAs, there are 63 Primary Urban Areas in the UK – 55 in England, three in Wales, four in Scotland and one in Northern Ireland – down from the 2005 list of 64.
  • Three new cities are added. Basildon, Exeter and Slough are included as PUAs.
  • Two cities fall out. Grimsby and Hastings fall below the workday population threshold and so are no longer classed among the list of largest concentrations of economic activity.
  • Two cities are incorporated into Manchester. Bolton and Rochdale now form part of Manchester PUA. Wigan remains a separate PUA as it is in a separate built-up area (BUA) to Manchester’s. Therefore Wigan continues to be a separate concentration of economic activity.
  • 11 cities have seen an alteration to their boundaries. These changes are the result of either physical changes to the BUAs or the lesser weight put on TTWAs in the updated approach.
    • Four cities – Swansea, Newport, Bournemouth and Manchester – have expanded to incorporate neighbouring local authorities
    • Five cities- Crawley, Blackpool, Reading, Liverpool and Glasgow – have lost one local authority.
    • London has changed shape as a result of its revised BUA. Dacorum and Mole Valley are excluded, and Hertsmere is included.
    • Belfast also sees a change to its boundaries as a result of local government reorganisation in Northern Ireland.