Symbiotic environment research of space structure in small and medium cities on basis of symbiosis theory

Twenty-first century is called "an urban century". The rapid urbanization and various urban problems brought by it have become the most serious challenge faced by our country. At present, a domestic multi-level urban system is formulated, with big cities as centers, small and medium cities as backbones, and small towns as foundations. In 2010, by number one document, central government has taken "focus on developing small and medium cities and center towns" as an important method to carry out urbanization, and take loosing residence restriction as a supplementary method. The increasing urban population results in continuous expanding of urban space, thus the development of small and medium cities plays an important role in the process of urbanization, and they also contribute a lot to coordinated development among interregional cities. Symbiotic environment, symbiotic unit and symbiotic mode are three main factors of symbiosis theory. As a sustainable developing biological theory, symbiosis theory is widely used in micro-economics, regional economics, sociology and architecture, and its theoretical system plays a very important role in constructing more scientific academic frame in applied sciences. By introducing symbiosis theory into urban planning, we can install a space structure "symbiotic system" in small and medium cities, aiming at coordinated development among regions. It will focus on analyzing symbiotic environment which includes economic background and market mechanism, globalization and informationization, urban policies and systems, analyzing the deep influence and significant meaning on urban space structure caused by changes of symbiotic environment, and proposing several devices on how urban space structure can make use of symbiotic environment.