Shaping ideal cities: the graph representation of the urban utopia

TL;DR

This paper introduces a novel graph-based method to analyze urban layouts, comparing historic city structures and highlighting the importance of irregular street patterns for connectivity and accessibility.

Contribution

It develops a new approach to construct urban graphs from Euclidean spaces and line graphs, extending space syntax analysis with spectral and asymmetry measures.

Findings

Irregular street patterns enhance connectivity and accessibility.

Peripheral streets play a crucial role in urban connectivity.

Historic cities share similar spectral and asymmetry properties.

Abstract

The ideal Renaissance city is designed as a star-shaped fortress, where the streets and squares are organized to speed the movement of people and soldiers. Symmetry and accessibility represent the key features for the organization of the urban space. The resulting city is hierarchized and does not always guarantee an optimal degree of connectivity. Taking the baton from the work done by space syntax in the definition of properties of spatial graph representation, we introduce a method to compute urban graphs from the Euclidean representation, the corresponding line graph and the contraction of nodes with the same urban function. We analyze the urban graphs of five historic cities: Vitry le Fran\c{c}ois, Avola, Neuf Brisach, Grammichele and Palmanova and compare the analysis restults with the corresponding results from space syntax. Analysis of the spectral gap and the relative asymmetry distribution show a similar structure for these cities. The irregular or reticular housing structure seems to ensure connectivity and accessibility more than the regular grids. However connectivity is ensured by the most peripheral streets, which in the space syntax representation play a marginal role.