30 June 2021

Applied Network Science: “Urban spatial order: street network orientation, configuration, and entropy”

Figures 4 and 5 put Chicago’s low entropy and Charlotte’s high entropy in perspective. Of these 100 cities, Chicago exhibits the closest approximation of a single perfect grid with the majority of its streets falling into just four bins centered on 0°, 90°, 180°, and 270°. Its φ = 0.90, suggesting it is 90% of the way between perfect disorder and a single perfect grid, somewhat remarkable for such a large city. Most American cities’ polar histograms similarly tend to cluster in at least a rough, approximate way. Charlotte, Rome, and São Paulo, meanwhile, have nearly uniform distributions of street orientations around the compass. Rather than one or two primary orthogonal grids organizing city circulation, their streets run more evenly in every direction.

Most of the North American cities lie near each other in three adjacent clusters (red, orange, and blue), which contain grid-like—and almost exclusively North American—cities. The orange cluster represents relatively dense, gridded cities like Chicago, Portland, Vancouver, and Manhattan. The blue cluster contains less-perfectly gridded US cities, typified by San Francisco and Washington (plus, interestingly, Buenos Aires). The red cluster represents sprawling but relatively low-entropy cities like Los Angeles, Phoenix, and Las Vegas. Sprawling, high-entropy Charlotte is in a separate cluster (alongside Honolulu) dominated by cities that developed at least in part under the auspices of twentieth century communism, including Moscow, Kiev, Warsaw, Prague, Berlin, Kabul, Pyongyang, and Ulaanbaatar. Beijing and Shanghai are alone in their own cluster, more dissimilar from the other study sites. The dark gray cluster comprises the three cities with the most circuitous networks: Caracas, Hong Kong, and Sarajevo. While the US cities tend to group together in the red, orange, and blue clusters, the other world regions’ cities tend to distribute more evenly across the green, purple, and light gray clusters.

Geoff Boeing

Interesting study into the structure of street networks in cities across the globe. The conclusions are roughly in line with previous expectations: North-American cities generally have neatly ordered, grid-like street orientations, owing to their relatively short history and highly centralized planning, while the rest of the world is much more varied, combining different cultures and historical periods into their current street layout. Cool graphics aside, this aspect should be high on the list of priorities for the people designing self-driving cars: an AI system trained on the highly regular grid of US cities will likely have a tough time navigating Singapore, Rome, or São Paulo.

Street networks and corresponding polar histograms for Manhattan and Boston
Fig. 3: Street networks and corresponding polar histograms for Manhattan and Boston. On the left, Manhattan’s 29° angled grid originates from the New York Commissioners’ Plan of 1811, which laid out its iconic 800-ft × 200-ft blocks. Broadway weaves diagonally across it, revealing the path dependence of the old Wickquasgeck Trail’s vestiges, by which Native Americans traversed the island long before the first Dutch colonists arrived. On the right, Boston features a grid in some neighborhoods like the Back Bay and South Boston, but they tend to not align with one another, resulting in the polar histogram’s jumble of competing orientations. Furthermore, the grids are not ubiquitous and Boston’s other streets wind in various directions, resulting from its age (old by American standards), terrain (relatively hilly), and historical annexation of various independent towns with their own pre-existing street networks.

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