This paper presents a simple tool for deciding land attribute plot ratios by defining elementary entities and their relationships from the viewpoint of a complex adaptive system. Each entity in this case, a block in the city, is described according to its condition and potential for development, such as land function, accessibility, landscape control, and so on. This not only provides a rich yet subtle identification of each entity, but also creates the basis to establish dynamic interconnections between them. The similarity coefficient, calculated by the comparison between the different blocks factors fits well with the explanation of the spontaneous development of the city. The weight of every factor and the threshold of the similarity coefficient are both set as variables, with the optimized value recommended as a default, which ensures a multitudinal application of this software with a focus on different aspects of urban planning. The resultant self-regulatory system with flexible input is not only a credible tool for deriving plot ratios, but also an effective platform to activate urban design creations. The system, as a socio-technical tool, enhances the essential process of urban self-organization and hetero-organization.