Constrained Cellular Automata for Modelling Sustainable Urban Forms

Cellular Automata (CA) have attracted growing attention in urban simulation because of their capability in spatial modelling which is not fully developed in GIS. This paper discusses how cellular automata (CA) which is increasingly used in urban simulation can be extended and integrated with GIS to help planners in the search for sustainable urban forms. A constrained cellular automaton is developed to produce optimal development patterns and thus reduce wasteful use of land resources. The cellular automaton is built within a grid GIS system to facilitate easy access to GIS databases for constructing the constraints. The essence of the model is that constraint space is used to regulate cellular space. Local, regional and global constraints play equally important roles in affecting the modelling results. Agricultural suitability, available land resource and economic and population growth could be used as key constraints. The paper discusses how to combine these constraints in CA modelling to enhance the efficiency in using land resources. In addition, ‘grey’ cells are defined to represent the continuous degrees or percentages of urban land development during the iterations of modelling for more accurate results. The model can be easily controlled by the parameter k using a power transformation function for calculating constraint scores. The CA model can be used as a useful planning tool to test the effects of different scenarios of urban development. The protection of valuable agricultural land is important in many developing countries where cities are growing rapidly. In China, some cities are expanding without properly considering land suitability and environmental impacts. Recent rapid land development has been accompanied by the loss of large amount of agricultural land. This study demonstrates that CA can be used to simulate urban development based on constraints that reflect our environmental concerns. The objective is to produce sustainable urban forms as alternatives to the existing development patterns. The study has suggested that CA can be used as a useful planning tool to model urban development under complicated and changeable environmental factors.