Constrained Cellular Automata for modelling sustainable urban forms

Abstract

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 automation is developed to produce optimal development patterns and thus reduce wasteful use of land resources. The cellular automation is built within a grid-GIS system to facilitate easy access to GIS databases for constructuring 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.

單元自動演化ＣＡ可以大大增強ＧＩＳ的空間模型能力，在國外被越來越多地應用于城市發展演化過程的模擬。本文探討了如何通過ＣＡ與ＧＩＳ的結合來進行可持續土地發展規劃的新方法。提出了基于約束性的ＣＡ模型，具體分析了局部、區域以及全局約束性對ＣＡ模型結果的影響。并將灰度的概念引進ＣＡ模型中來反映狀態連續的變化，克服常規ＣＡ模型的缺陷。將該模型應用于珠江三角洲地區來獲得合理的城市發展空間布局，取得了較好的效果