Agglomeration

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The measured tendency for firms and workers to be more productive when there are more of them nearby. It is the reason cities exist at all, and it is a network effect rather than a design property: the value of being in a city comes from the other people already in it, which is why it cannot be laid out in advance the way a road can. The empirical literature summarised by Rosenthal and Strange puts the elasticity of productivity with respect to city size in a fairly narrow band — roughly 3 to 8 per cent for a doubling of size in most estimates, with French and US wage-elasticity estimates near 0.03 and 0.043. Three mechanisms are usually distinguished: sharing of inputs and infrastructure, better matching between workers and jobs, and learning through proximity. Two features matter for this Journey. The effects decay steeply with distance — they are neighbourhood-scale, not metropolitan-scale — and they are a property of accumulated density, which is exactly what a new-build city does not have on opening day.

A node is not a place. Drawing it on a map would assert something about the world that no stored fact supports.