the gauteng spatial development framework - Gauteng Online

THE BID-RENT MODELThe Bid-Rent Model is a computer (GIS) based model that provides a spatial depiction ofa range of relative values of an area. The model, as it has been developed for the currentprocess, draws on both desirability value, an approximate measure of development demand,and developability value, an indication of the overall suitability of an area for development.The basis of the Bid-Rent Model lies with 'grid' of 10m x 10m cells superimposed over theGSDF study area. Base data layers are filtered through this grid, resulting in each cell havinga specific value corresponding to each data layer.The resulting grid of cells, the basis of the model, serves as a basis for elaborating theproposed framework (structure/ lattice) as a whole (i.e. in terms of a specific developmentscenario or trend/strategy), or for specific development queries and analysis.Bid-rent theory is used in urban economics to model urban activity patterns, and intensitiesof activity, according to the land value potential of a place as informed by how much acertain use would bid for a piece of land relative to the prices other land-uses would bid.Thus, at an epicentre of very high land value within a given spatial extent (notionally referredto as the Peak Land Value Intersection of any particular district), retail may typically bidextremely high at and over a very short distance from this epicentre; office uses may bidless but over a wider area from the epicentre; residential, in turn, may bid less but over amuch wider distance; and industrial, for its part, may bid least and be placed, by the propertyvalues, furthest away from the epicentre. The resultant value-gradient from these graphsrepresents what is referred to as the 'bid-rent curve' of a particular point or district.Effectively, the urban potential of any given point is indicated relative to its existing positionin the urban structure, its urban fundamentals (such as visibility and access), and the natureof the infrastructural investments in that area.This simply gives an indication of what might be expected, in urban performance terms,of an area in the existing circum-stances. It is then possible to test, in 'if-then' terms, whatthe result may be of various interventions into that area, say, in the form of a new highwayinterchange, or a new station or road link.ANNEXURE A: THE 5 GIS-BASED MODELSTHE ROLE OF THE MODELThe model is intended to guide the design process by suggesting areas of higher potentialenergy and intensity, and provide some direction to the determination of specific functionaluses, or the degree of mix of uses. It can also serve as a basis for longer-term strategies forthe development and release of land.The Bid-Rent Model has been developed to describe an indicative urban potential of anygiven point within the GCR expressed, notionally, in 'bid-rent' terms. It is a model derivedto indicate relative urban development value rather than an indicative land value and shouldbe regarded in these terms only.One is thus able, for example to identify those areas that may not be achieving theirurban potential at present, postulate why this may be, and test whether any particularprogramme of intervention would assist it in achieving more. Similarly, by cross- referencingwith the connectivity model, one may identify areas of dislocation and test the efficacy,indicative with the Bid-Rent Model, of various spatial interventions to rectify this.The diagram alongside reflects the overall structure of the Bid-Rent Model, showing thedifferent layers utilised in formulating the cellular variables across the study area.As reflected in the diagram, there are two distinct 'indices' around which the Bid-RentModel has been structured; one that defines an index of 'desirability' in the sense of creating115 GAUTENG SPATIAL DEVELOPMENT FRAMEWORK 2011 GAUTENG GROWTH AND DEVELOPMENT AGENCY