GeoJournal 59: 167, 2004.© 2004 Kluwer Academic Publishers. Printed in the Netherlands.

167

Guest editorial: Systems modelling across geography’s interface

Richard Thomas1 & Yee Leung2

1School of Geography, The University of Manchester, Manchester, U.K.2Department of Geography and Resource Management, The Chinese University of Hong Kong, Hong Kong

This special issue consists of seven papers originally presen-ted to the Commission on Modelling Geographical Systems(CMGS) sessions at the International Geographical UnionCongress in Durban, August, 2002. This meeting was or-ganised to explore communality between modelling stylesin human and physical geography at a time when researchin these sub-disciplines often follows independent agendas.In this respect, systems modelling offers opportunities fora degree of contextual and technical integration. Under-standing the effects of current issues of common concern,like the socio-economic consequences of climatic change,or the environmental impacts of major planning projects, isassisted by this interdisciplinary approach. Moreover, theincreasing application of remote sensing to monitoring geo-graphical systems is both bridging gaps in GIS data handlingand beginning to provide a meeting place for the social andphysical sciences (Longley, 2002). This volume, therefore,addresses a range of problems that straddle this interfacewithin the broad ambit provided by the systems perspective.

The papers are organised to reflect recurring themesin the design and implementation of geographical systems(Huggett, 1980). The first of these addresses the analysis ofspatial structure which is often observed to vary relativelyslowly through time and, consequently, is assumed to re-strict the range of behaviours posited for the phenomenon ofinterest (Thomas, 1993). The two papers in this set focus onthe role of land-use distribution as such a spatial constraint.Guermond et al., for example, demonstrate how cellularautomata programs are relevant to both understanding thehistorical evolution of urban land-use and the flow of run-offin a schematised drainage basin. The fundamental differencebetween the two programs is that, in urban system, spatialrelations are specified as distances whereas, in the drainagebasin, contiguity is the appropriate measure. In their paper,Samimi and Kraus apply regression procedures to remotesensing imagery to estimate the grazing capacity associ-ated with the biomass quantified for savannah ecosystemsin Southern Africa. Their results indicate how insufficientattention to grazing and fire management can cause thedegradation of soil and vegetation in such environments.

Within the bounds imposed by structure, the behaviourof a system is further conditioned by the set of relationshipsthat connect its component parts. In geography, this ideahas often been manifested by the construction of models topredict flows or rates of activity between a set of regionalpopulations according to their degree of spatial separation(Sen and Smith, 1996). The analysis of such interactions

provides the link between the second group of papers. First,Hyman and Mayhew present mathematical models wheresuch separation is visualised as a map transformation ofa time surface that assumes the cost of travel is differentin each direction. This scheme has relatively minimal datarequirements and is shown to be applicable to transport plan-ning problems associated with a variety of regional networkmetrics. In contrast, Weir-Smith’s concern is with socialinteraction. She analyses a national survey of drug sub-stance arrestees in South Africa to test the hypothesis thatthe activity and crime spaces of these individuals expand co-incidentally. The results highlight places where drugs mightbe expected to be obtained.

While applications of systems models often entail thereconstruction of past events to reproduce present condi-tions, the ability to predict remains the main motivationdriving their development. The third set of papers, there-fore, addresses this challenge of the future from a variety ofmethodological perspectives. Schwarz, for example, invest-igates the long-term behaviour of agricultural and aquaticecosystems that are subject to exploitation. He argues theirsustainability is indicated by the existence of a stable equi-librium in the presence of human disturbances like planting,fertilising or feeding. In contrast, unstable systems are seento degrade to an unsustainable low yield state. Wang et al.adopt the notion of an economic equilibrium to tackle theplanned sequencing of new water supplies for the districtsof Hubei Province, China. Their dynamic allocation modeldemonstrates how the optimum allocation arises when themarginal revenue for water in each district is equal and theeconomic benefit to all users is maximised. Finally, Chubeyand Hathout develop statistical procedures that combineMarkovian analysis and logistic regression to estimate themagnitude and spatial extent of future flood risk. Their ap-plication is for the Red River in Manitoba but, following thefundamental prerequisite of geographical systems analysis,their method is easily transferable to other areas.

References

Huggett R.J., 1980: Systems analysis in geography. OUP, Oxford.Longley P.A., 2002: Geographical Information Systems: will develop-

ments in urban remote sensing and GIS lead to better urban geography?Progress in Human Geography 26: 231–239.

Sen A. and Smith T.E., 1996: Gravity models of spatial interactionbehaviour. Springer-Verlag, Berlin.

Thomas R.W., 1993: Quantitative methods: relaxing the constraints. Pro-gress in Human Geography 17: 247–256.