Monocentric urban simulation models: getting closer to fractal properties and landscape representation

Scientific Conference (2015, November)

Urban growth generates spatial patterns that in many cases demonstrate fractal properties. Geocomputational models, particularly cellular automata and spatial agent-based simulation models have been used ... [more ▼]

Urban growth generates spatial patterns that in many cases demonstrate fractal properties. Geocomputational models, particularly cellular automata and spatial agent-based simulation models have been used over the last 20 years to generate urbanisation patterns with the aim to replicate at best observed expansion footprints, including matching observed and simulated fractal dimensions. In applied cases, with the addition of constraints at multiple scales (land constraints, threshold per zones, etc.) simulation models seem to perform rather well and obtain sound urban fractal dimensions. Models that are more parsimonious in parameters however do not seem to perform as well. Exceptions are those models directly inspired from physics such as DLA (Diffusion Limited Aggregation) or DBM (Dielectric Breakdown Models) but these are frustrating when it comes to behavioural or economic interpretation. Models with explicit micro-economic component in a monocentric setting also seem to lag behind in terms of fractal performance: unless exogenous spatial heterogeneity is provided, the spatial outcome of these models is too homogenous to resemble real cities, despite agglomeration and dispersion processes at neighbourhood scale and despite the self-emergence of road networks and subsequent open land lock-ins. Rather than resolving to exogenous polycentric setting or exogenous stochasticity that would provide better looking outcomes, we investigate this insatisfaction by exploring the results of an augmented micro-economic simulation model on a theoretical monocentric space. The innovations are brought along three rationales: Firstly, an assumption is made that the length of the infrastructure network should feed back into households budget. Cities cannot expand too quickly not only because of unitary commuting costs but also infrastructure costs. We therefore implement an infrastructure tax that should lead to agglomeration or a more efficient generation of roads from the city perspective. Secondly, we assume that the infill of undeveloped spaces by new residents is limited by residents who settled earlier in the city and refuse important utility losses in terms of open green space. This leads to relaxing the assumption of a dynamic adaptation of rents and building stock trough time. Free entry and placement is somehow limited by a public authority that keeps utility at its higher possible state at each time step. Thirdly, we abandon the assumption that neighbourhood quality is related to the density of available activities or the density of green space within a given neighbourhood, but replace this with the access to a diversity of urban and green opportunities depending on their use frequency (daily walk, playground, hiking in forest,…). This is a very important change in geocomputational terms since simple focal functions can no longer be used to represent externalities in simulation models. The gradual construction of roads and houses change gradually the nature of the landscape and the value taken out of it, typically by dividing green patches into parts, creating detours to access bigger parks, shadowing effects, etc. In addition, this requires that landscape objects are represented as vectors, not cells, which is a second important change in geocomputational terms. To some extent this brings urban simulation models closer to landscape ecology and graph-based approaches. In this paper we explore and contrast the effects of the three mechanisms mentioned above on the resulting urban morphology. [less ▲]

Emergence of leapfrogging from residential choice with endogenous green space: analytical results

in Journal of Regional Science (2015), 55(3), 491-512

Leapfrog development is a typical form of sprawl. This paper aims at analyzing the existence, size, and persistence of leapfrogging in a dynamic urban economic model with endogenous green amenities. We ... [more ▼]

Leapfrog development is a typical form of sprawl. This paper aims at analyzing the existence, size, and persistence of leapfrogging in a dynamic urban economic model with endogenous green amenities. We analyze whether incoming households choose to settle at the fringe of the city or to jump further away depending on their preferences and the structure of the city. We first provide an analytical treatment of the conditions and characteristics under which a first leapfrog occurs and show how the optimal choice is affected by the size of the city, income, commuting costs, as well as the size of the area where green amenities are considered. We then study how further leapfrogging and multiple urban rings may appear and be maintained in the long-run equilibrium, and how infill processes take place through time. [less ▲]

Housing land transaction data and structural econometric estimation of preference parameters for urban economic simulation models

in Data in Brief (2015), 5

This paper describes a dataset of 6284 land transactions prices and plot surfaces in 3 medium-sized cities in France (Besançon, Dijon and Brest). The dataset includes road accessibility as obtained from a ... [more ▼]

This paper describes a dataset of 6284 land transactions prices and plot surfaces in 3 medium-sized cities in France (Besançon, Dijon and Brest). The dataset includes road accessibility as obtained from a minimization algorithm, and the amount of green space available to households in the neighborhood of the transactions, as evaluated from a land cover dataset. Further to the data presentation, the paper describes how these variables can be used to estimate the non-observable parameters of a residential choice function explicitly derived from a microeconomic model. The estimates are used by Caruso et al. (2015) to run a calibrated microeconomic urban growth simulation model where households are assumed to trade-off accessibility and local green space amenities. [less ▲]

Emergence of scattered and leapfrog urban development from analytical results to complex simulation outputs with realistic calibration

Scientific Conference (2013)

Morphological similarities between DBM and a microeconomic model of sprawl

in Journal of Geographical Systems (2011), 13(1), 31-48

We present a model that simulates the growth of a metropolitan area on a 2D lattice. The model is dynamic and based on microeconomics. Households show preferences for nearby open-spaces and neighbourhood ... [more ▼]

We present a model that simulates the growth of a metropolitan area on a 2D lattice. The model is dynamic and based on microeconomics. Households show preferences for nearby open-spaces and neighbourhood density. They compete on the land market. They travel along a road network to access the CBD. A planner ensures the connectedness and maintenance of the road network. The spatial pattern of houses, green-spaces and road network self-organises, emerging from agents individualistic decisions. We perform several simulations and vary residential preferences. Our results show morphologies and transition phases that are similar to Dieletric Breakdown Models (DBM). Such similarities were observed earlier by other authors, but we show here that it can be deducted from the functionning of the land market and thus explicitly connected to urban economic theory. [less ▲]

S-GHOST: Un modèle d'auto-organisation de l'étalement urbain et du réseau de transport

in Antoni, Jean-Philippe (Ed.) Modéliser la ville: formes urbaines et politiques de transport (2011)

The emergence of leapfrogging in an urban growth model combining an economic approach and cellular automata

Scientific Conference (2009)

Surprising similarities between DBM models and an economic geography model of city growth

Scientific Conference (2008)