Long model, also called long description, is a system with a great deal of order and little randomness. A long model morphogenesis occurs only where the rules restricting the random process are too many or too global. The higher the proportion of possible spatial relations specified by the rules, and the more global those rules, and less the process has morphogenetic potential, and the more it will conserve the form given by the rules. See: Short model.
Hillier, B. & Hanson, J. (1984), The Social Logic of Space, Cambridge University Press: Cambridge. pp.12-13;
Hillier, B. (1996, 2007), Space is the Machine: A Configurational Theory of Architecture. Space Syntax: London, UK. pp.192