The 15 min non-city – a theoretical follow-up

I have enjoyed reading the comments about the 15 minute city. They raise interesting points, and it is worth – briefly – going into a bit of theory.

Almost a century ago a geographer called Christaller noted some regularities in the way retail activity and services deployed across cities and regions1.

Assuming an even density of people living across a city area, and no major physical barriers, he noted that everyday services, those that we use frequently (like bakers, small grocery stores, local libraries), tend to locate at regular intervals, equivalent to, let’s say, about 15 minutes walk. That is because there are enough customers within a 15 minute radius to allow these businesses to thrive, and, conversely, customers are willing to walk about 15 minutes to get to these facilities. So these businesses could survive in a 15 minute city.

Other services and facilities (such as, maybe, general practice doctors, larger grocery stores, malls, dentists, book stores…) locate at about 30 minute intervals: fewer people use them, or they use them less frequently. These businesses therefore need to draw upon a larger market area, one with a larger radius, to survive; conversely, customers travel further to these services because they use them less often. So these businesses need a 30 minute city.

Finally, there are services we use very infrequently (or which are used by very few people), such as passport offices, the planning department, lawyers and accountants . These services tend to locate at even greater intervals, say an hour or so. Why? Because they need to draw upon an even larger market area, and their customers, who use them even less frequently, are ready to travel further. So these businesses need a 60 minute city.

A typical sketch of market areas. ‘Low order’ settlements would be the core of 15 minute neighbourhoods, and the ‘high order’ ones the core of 30 minute neighbourhoods. Source: https://s-cool.co.uk/a-level/geography/urban-profiles/revise-it/central-place-and-bid-rent-theories

This very basic argument – which sketches out Christallerian location theory – explains why the 15 minute city is impossible – or at least incompatible with theory (and indeed with most people’s casual observation of actual cities). Whilst the precise geometry of neighbourhoods and settlements rarely fits Christaller’s predictions, his basic reasoning is very useful to understand some of the characteristics of neighbourhoods and wider settlements.

There is another reason why 15 minute cities won’t work. Christaller’s theory focuses only on services and facilities that people use: but what about the production of goods and services? We can’t have a car factory, a bicycle maker, a university, an airport, or a hospital in every neighbourhood. These units of production all generate internal economies of scale (i.e. they need to be quite large to function). Furthermore, goods and services can often be distributed (i.e delivered by truck – which happens for bikes and cars -, or people travel across the city to consume them where they are produced – which happens for universities, airport services, and hospitals).

So, these production facilities will not be distributed evenly across all neighbourhoods, and will not necessarily follow the patterns set out by Christaller: they will be concentrated in one or two specific neighbourhoods (maybe those best accessible to a port, to railways, or where a large piece of land was available). People who want to work, say, in a hospital or aeroplane factory will need to travel there from across town. It would be unfair for these hospital or factory jobs to be reserved only for neighbourhood residents!

Many units of production (such as hospital) can’t be subdivided. If anyone from outside the 15 minute neighbourhood wants to work there, they’ll need to travel

One apparent solution is for all workers to live close to their place of work. But what happens when families grow and people want to change houses, or when careers develop and people want to change jobs? Even if we miraculously begin with a 15 minute city, where all people live and work locally, this would rapidly evolve as people’s lives, careers, and aspirations develop.

These two basic reasons – i) different market areas for different types of facilities; and ii) production processes generating internal economies of scale (and therefore not being spread evenly across neighbourhoods) – explain why, from the perspective of economic geography, the 15 minute city is a non-starter.

If we alter the concept, and speak of a 15 minute neighbourhood, that is easier to conceive of, so long as we realise that a 15 minute neighbourhood will only contain a limited array of services and facilities (those that can survive whilst only drawing customers from within a 15 minute radius). A 15 minute neighbourhood may or may not contain large production facilities (and if it does, it would not have much to do with the 15 minute market radius!).

To access a variety of jobs and to access specialised services and facilities (which are what differentiates cities from villages), people from most areas in a city will need to travel well beyond the confines of their 15 minute neighbourhood.

I hope this clarifies – from a slightly more conceptual perspective – my point about 15 minute cities not being cities.

1 It should be noted, as Trevor Barnes has elaborated, that Christaller developed this theory (which was derived from observation and emprics) whilst planning Nazi expansion towards the east . But, as Alan Scott has argued, this does not mean that his insights are not important: it does mean that their initial application was to plan for settlement of these vast areas.

Published by Richard Shearmur

I am a professor at McGill's School of Urban Planning. I perform research on innovation, on how we locate work activities (in a world where people often work from many places), and on urban and regional economic geography. I used to work in real-estate, and teach a course on this. I am an urban planner, member of the Ordre des Urbanistes du Québec and of the Canadian institute of Planners.

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