Featured Graphic. Mapping Shifting Hierarchical and Regional Tendencies in an Urban Network through Alluvial Diagrams
使用冲积图展示全球生产性服务企业形成的跨国城市网络中，城市集群的层级和区域趋势在2000、2004和2010年的演变，帮助理解城市地位的动态变化。
We employ alluvial diagrams (Rosvall and Bergstrom, 2010) to map the evolution of interweaving hierarchical and regional tendencies in the transnational urban networks created by globalizing producer services firms (Derudder et al., 2003; Taylor et al., 2012). We first applied a hierarchical cluster analysis to 139 leading cities for 2000, 2004 and 2010 respectively, whereby cities are grouped based on their portfolio of firms. In the alluvial diagram, individual blocks represent city clusters, and in each year blocks are ranked hierarchically (i.e. from top to bottom based on the average number of firms per member city). Clusters are named after the formative type of member city, e.g. the continued presence of hierarchically ordered and regionally coherent clusters of United States cities. Horizontal streams connect preceding and succeeding clusters based on shared city membership, which allows tracing how individual as well as groups of cities’ positions evolve over time. The width of a streamline is proportional to the number of cities with the corresponding membership change. More technical details can be found in Liu et al. (2012).