Integrating Urbanization and Eco-Environment Systems: A Case Study of the Beijing-Tianjin-Hebei Region Li Tian * , Gaofeng Xu, Chenjing Fan, Yue Zhang *, Chaolin Gu and Yang Zhang Department of Urban Planning, Tsinghua University, Beijing 100084, China; xugf16@mails.tsinghua.edu.cn (G.X....