Polycentricity and polarisation
Complex cities are constrained in their ability to grow outwards by Green Belt policies (and as we write elsewhere, this doesn’t seem likely to change). This has two main spatial consequences – firstly, development ‘leapfrogs’ the Green Belt and is relocated to towns beyond the protected zone, and secondly, rising land prices in the core city force developers to use land more efficiently, typically by seeking to build upwards.
However, building upwards is not straightforward. Local authorities need to be persuaded of two things. Firstly, that the higher density which results from taller buildings will not place undue pressure on local services and infrastructure. And secondly, that taller buildings will not damage the character of an existing area – by being out of scale, or simply very prominent.
These difficulties tend to point towards the same practical result.
Density is increased where it is embraced by the determining authority, and predominantly only where new infrastructure is also provided (and indeed, new development is often asked to contribute towards the cost of that infrastructure). This leads to new development being concentrated at (and indeed above) transport nodes.
And concerns over the visual impact, scale and character of high density development tend to cause such development to be concentrated in clusters – most notably in the City of London.
These two effects are symbiotic – transport nodes have high footfall and a certain bustle about them compared with their surrounding areas, which influences the character of the area, making higher density development feel more appropriate and easier to justify.
Furthermore, the vitality arising from higher density development can help support placemaking and economic activity, including retail and office uses. This explains why there is a natural affinity between many regeneration schemes and public transport nodes, such as Birmingham’s Grand Central, and why mixed use schemes are so heavily promoted at such locations.
But in the UK’s larger cities, especially London, the complexity of the transport network leads to a polycentric development pattern, with clusters of high(er) rise buildings in well-connected locations well beyond the urban core. Tall buildings used to be the preserve of the city centre, but in the last 10-20 years well-connected London districts such as Croydon, Elephant & Castle, and Stratford have increasingly been creating tall building clusters. It’s often been said that London is a city of villages. Now, it is becoming a city of towns.
But what about the rest of the urban area? More suburban areas will perhaps feel sleepier by contrast. Less well connected, the suburbs may form the rather neglected hinterland to these new cities-within-a-city. This might be welcome to residents of those suburbs, but it carries risks as well – that investment is diverted from suburbs to district centres; or that low density development cannot sustain very local services (a corner shop or pub here or there), leading to suburban areas which flake and crumble while the district core bustles. With such scarcity of land, many of these locations are relatively accessible, and could be used far more effectively to accommodate growth.
Or maybe it will be the other way round? The space that suburban homes afford may become increasingly valued compared with smaller, more densely-packed homes close to transport nodes, or to homes much further afield outside the city with (as we have written elsewhere) longer commute times. The older city dwellers get, the more affluent they get, so the more they might prize the suburban vibe over the urban vibe. One possible outcome, if present trends continue, is that cities internally become more polarised between their high-rise polycentric cores and their low-rise suburban peripheries, for better or for worse.