The hierarchy includes : Urban Master Plan, District Plan, Designation of Development Site, Comprehensive Plan for Development Project, and Detailed Plan for Development Project. For example, the Urban Master Plan determines the long term vision for the city; the District Plan, reflecting the Urban Master Plan, determines the direction of the development of each sector identified in the Master Plan. Development sites are determined by the Designation of Development Sites Plan. Comprehensive Plans can be seen as the basic plan for development projects, including scale, boundary, and specific locations. The Detailed Plan includes arrangement of facilities and mitigation measures for specific projects outlined in the Comprehensive Plan. This interrelationship of plans means that failure of environmental consideration at one level can have knock-on effects down the system, and consequently it is important to have PERS at each level. However, it was only applied to the Detailed Plan for Development Project (see Table 3). In addition, it was difficult to reflect the results of PERS into plans because it was usually conducted too late in the planning process. Thus, it was also difficult to consider environmental details during the earlier stages of the planning process (Song et al., 2003).