Agent-Based Modelling for Interdisciplinary Geographical Enquiry

Bruce Rhoads argued that;

“The time has come for geography to fulfil its potential by adopting a position of intellectual leadership in the realm of interconnections between human and biophysical systems.”

Many areas of scientific endeavour are currently attempting to do the same and interdisciplinarity has become a big buzzword. Modelling has become a common tool for this interdisciplinary study (for example ecological-economic models), with several different approaches available. Increases in computing power and the arrival of object-oriented programming have led to the rise of agent-based modelling (also termed individual-based and discrete element).

In their latest paper in Geoforum, Bithell et al. propose this form of modelling, with its “rich diversity of approaches”, as an opportune way to explore the interactions of social and environmental processes in Geography. The authors illustrate the potential of this form of modelling by providing outlines of individual-based models from hydrology, geomorphology, ecology and land-use change (the latter of which I have tried to turn my hand to). The advantages of agent-based modelling, the authors suggest, include the ability to represent

  1. agents as embedded within their environment,
  2. agents as able to perceive both their internal state and the state of their environment
  3. agents that may interact with one another in a non-homogeneous manner
  4. agents that can take action to change both their relationships with other agents and their environment
  5. agents that can retain a ‘memory’ of a history of past events.

However the development of these representation can be a challenging task as I found during my PhD modelling exploits, and requires a ‘diversity of resources’. When representing human agents these resources include past population censuses, surveys and interviews of contemporary populations, and theoretical understanding of social, cultural and economic behaviour from the literature. In my modelling of a contemporary population I used interviews and theoretical understanding from the literature and found that, whilst more resource intensive, actually going to speak with those being represented in the model was by far more useful (and actually revealed the deficiencies of accepted theories).

In their discussion, Bithell et al. consider the problems of representing social structures within and an individual-based model suggesting that;

“simulation of social structure may be a case of equipping model agents with the right set of tools to allow perception of, and interaction with, dynamic structures both social and environmental at scales much larger than individual agents”.

Thus, the suggestion is that individually-based models of this type may need some form of hierarchical representation.

Importantly I think, the authors also briefly highlight the reflexive nature of agent-based models of human populations. This reflexivity occurs of the model is embedded within the society which it represents, thus potentially modifying the structure of system it represents. This situation has parallels with Hacking’s ‘looping effect’ that I’ll write about more another time. Bithell et al. suggest that this reflexive nature may, in the end, limit the questions that such models can hope meaningfully address. However, this does not prevent them from concluding;

“The complex intertwined networks of physical, ecological and social systems that govern human attachment to, and exploitation of, particular places (including, perhaps, the Earth itself) may seem an intractable problem to study, but these methods have the potential to throw some light on the obscurity; and, indeed, to permit geographers to renew their exploration of space–time geographies.”

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