The design of the DELTA land-use modelling package

In this paper the design of a new land-use modelling package, DELTA, is described. The focus is on the thinking behind the design and the model characteristics that have resulted rather than on the formal mathematical specification. The package has been designed to link with any appropriate transport model so as to create a dynamic system for land use - transport interaction modelling. DELTA itself is a model of a variety of different processes of change in an urban system. It is intended to represent these processes of change over a succession of relatively short (one-year or two-year) periods. The different processes are fairly weakly linked to each other within any one time period but important feedback effects, both positive and negative, come into play over time, both within DELTA and through interaction with transport. The model design is not based on any one key theoretical concept, but on the view that differing concepts are needed to represent the various processes. The processes modelled can be divided into those which primarily affect spaces and those which primarily affect activities. Those modelling change in spaces predict changes in the quantity and quality of floor-space available for occupation. Those referring to activities deal with: (a) household transitions and employment growth or decline; (b) location or relocation, and competition for space (the property market); and (c) the employment status of individuals. The location or relocation model is the main locus of interactions both between activities and space and between land use and transport. The influence of transport operates through sets of accessibility measures and through environmental variables.