SN: I have to admit, the physicists came up with a catchy phrase, “urban DMA”. See article excerpts below for a quick explanation.
Great cities and neighbourhoods always have a particular kind of urban intensity - what we might call the “character”, “buzz” or “atmosphere” that emerges over time. While unique in many ways, great cities also have certain things in common. One way to understand these properties is to think about a city’s “urban DMA” - its density, mix and access.
Access is about how we get around in the city. How do we make connections between where we are and where we want or need to be? At a neighbourhood scale access is primarily about “walkability”; at larger scales we depend on a mix of cars, cycling and public transport. But access means nothing if there is nowhere to go – the synergy with density and mix is everything.
Mix is about the differences and juxtapositions between activities, attractions and people. It’s not about diversity as spectacle, but a means of enabling encounters and flows between different categories of people, buildings and functions. Mix is about the alliances and synergies between home, work and play; between production, exchange and consumption.
Like density, mix can be uncomfortable; it means proximity to different kinds of people and practices. It means a layering of old and new buildings, of large and small buildings, and of large and small organisations.
There are dangers in an excess of some kinds of density, like the overcrowding of populations and the loss of light and air that comes with excessive building. There are many different kinds of densities - of residents, jobs, buildings, houses and street life. They interconnect, and they all matter.
The big question about density is: how much activity, how many people and how many buildings can be concentrated into one urban area?
Urban planning enables and constrains these dimensions of urban life. And unlike human DNA, urban DMA can be redesigned. If we want a healthy, creative, productive and low-carbon city - if we want “the buzz” - we need to reshape the urban DMA.