Co-evolution of density and topology in a simple model of city formation

TL;DR

This paper presents a simple model demonstrating how population density and road network topology co-evolve, reproducing key empirical features of city street networks and density distributions.

Contribution

It introduces a novel framework that explicitly models the interaction between road network topology and population density evolution.

Findings

Density profiles decrease exponentially from city centers.

High centrality nodes attract higher population density.

The core district size depends on transportation and rent costs.

Abstract

We study the influence that population density and the road network have on each others' growth and evolution. We use a simple model of formation and evolution of city roads which reproduces the most important empirical features of street networks in cities. Within this framework, we explicitely introduce the topology of the road network and analyze how it evolves and interact with the evolution of population density. We show that accessibility issues -pushing individuals to get closer to high centrality nodes- lead to high density regions and the appearance of densely populated centers. In particular, this model reproduces the empirical fact that the density profile decreases exponentially from a core district. In this simplified model, the size of the core district depends on the relative importance of transportation and rent costs.