Urban Modeling

Glossary Agent-Based Models (ABMs) A class of models developed since the 1980s which are based on representing objects and populations at an elemental or individualistic level which reflects behaviors of those objects through space and time. These models operate from the bottom up and sometimes generate emergent spatial and temporal patterns at more aggregate levels. Calibration The process of dimensioning a model in terms of finding a set of parameter values that enable the model to reproduce characteristics of the data in the most appropriate way. Calibration is not the same as validation which seeks to optimize a model’s goodness of fit to data, but often, these processes are equivalent. Cellular Automata (CA) A class of spatially disaggregate models, often pictured as being formed on a two-dimensional lattice of cells, where each cell represents a land use and embodying processes of change in the cellular state are determined in the local neighborhood of any and every cell. Such models can be seen as simplifications of agent-based models where the focus is on emergent spatial patterns through time. Complex Systems Systems that show surprising and unanticipated or ‘emergent’ behaviors as shown in patterns that arise at the aggregate level from the operation of system processes at the micro or agent level. Such systems are intrinsically unpredictable in an overall sense but can be fashioned in such a way that makes knowledge of them useful and certain. Cities are the archetypical example, but so too is the economy. Discrete Choice A development of computable microeconomic theory in which individuals maximize a utility, subject to constraints on their choices which can be tailored to reflect how decisions are made in complicated situations. Such models have been applied extensively in transportation modeling and have strong links to more aggregate maximization models as derived from spatial interaction and social physics. Land-Use Transport (LUT) Models A class of models that focus primarily on the way populations and employments locate in urban space consistent with the spatial interactions between different locations of these activities. These models usually simulate the city at a cross section in time and as such, bundle urban dynamics into equilibrium behaviors. Social Physics The application of ideas from classical ‘Newtonian’ physics to social systems usually in the form of analogies with Newton’s laws of motion as reflected in the concepts of potential energy and gravitational force. This lies at the heart of spatial interaction modeling but more recently such physics has been extended to embrace notions of complexity as reflected in scaling, self-organization, and the dynamics of far-fromequilibrium systems. Spatial Interaction Movements of goods, people, and information between different spatial locations, often referred to as origins and destinations, theorized and simulated using analogies with gravitational laws in physics. Such models form the basis of standard methods for describing and modeling interactions ranging from trip making in cities to long-range migration between cities. Urban Dynamics Representations of changes in urban spatial structure through time which embody a myriad of processes at work in cities on different, but often interlocking, time scales ranging from life cycle effects in buildings and populations to movements over space and time as reflected in spatial interactions. Urban Economics The development of microeconomic theory at the urban scale, following the tradition of the von Thunen model in which location and land rent are hypothesized as a function of distance or travel costs from some market center. The development of these ideas in the 1960s led to this branch of economics being called the New Urban Economics and more recently it has been extended using growth and trade theory. Urban Modeling The process of identifying appropriate theory, translating this into a mathematical or formal model, developing relevant computer programs, and then confronting the model with data so that it might be calibrated, validated, and verified prior to its use in prediction. Urban Models Representations of functions and processes which generate urban spatial structure in terms of land use, population, employment, and transportation, usually embodied in computer programs that enable location theories to be tested against data and predictions of future locational patterns to be generated.