Graph Representation of the 15-Minute City: A Comparison between Rome, London, and Paris

We studied the structure of the 15-minute city by measuring the distances from the services on spatial graphs. While the concept of the 15-minute city is rapidly spreading, its operative definition can be of help for planning and understanding the possibilities of the general idea. For three European cities (Rome, Paris, and London), we developed a method to calculate pedestrian travel time to reach services for all the possible paths on urban graphs, finding that the 15-minute city generally has multiple connected components and that the services have not necessarily been part of it. This algorithm was used to to make a quantitative comparison between the cities, showing that Paris and London have a stronger 15-minute characterization than Rome. By generalizing the method, it was possible to define a 15-minute urban index, which quantitatively characterizes this city feature. The results seem to be promising because, at the cost of the massive use of computational time, a digital model for the city can be generated: a planning tool to simulate urban solutions and a rigorous criterion for evaluating how much a city can be considered a 15-minute city.