The origin, spatial pattern, and evolution of urban system have been hot research issues in the field of urban system. In this study, the theory of "urban tree (UT)" was proposed to address these issues. The spatial pattern of urban system can be expressed by the phrase UT and the growth of the UT reflects the origin, spatial pattern, and evolution of urban system. Analysis of the UT growth can reveal the evolutionary mechanisms of the urban system. We present an UT resistance model to determine spatial extension in the evolutionary processes of urban system. The Thiessen polygon method and sp...
