The paradigm of pattern-based design has being widely adopted in the fields of software engineering (Gamma et al. 1994, Zhao et al. 2007a, 2007b), spatial information representation and reasoning (Kong and Zhang 2003) and data mining (Qian et al. 2004). The idea “design patterns” rooted in Chomsky’s “Generative Grammar” and formal language theory (1956, 1957), Simon’s “Hierarchy and Complexity” (1962, 1973) and Fu’s “Pattern Grammars” (1971, 1976), etc. These original and visionary works shed light on the research of theories and methodologies on “patterns” and “pattern-based design” with complexity theories, especially information theory of complex systems (Lindgren K 1988, 2003). However, in environmental planning and design, formal pattern-based design methodologies are still absent, although there are notable early explorations (Stiny 1972, Yessios C 1972, 1987, Alexander 1977). This paper proposes a formalized framework of the process and mechanics of pattern formation, in the context of physical planning and architectural design for 2D space layout. It discusses parsing and generation of such layout, on the basis of complex systems and the related information theory, design cognition and knowledge representation (Vries et al. 2010).