标题：Working together: the roles of geographic proximity, homophilic organizational characteristics, and neighborhood context in civic stewardship collaboration networks in Philadelphia and New York City
摘要：We examine networks of collaboration among civic environmental stewardship organizations in Philadelphia and New York City to understand which factors shape collaborative ties between organizations. Environmental issues in cities are increasingly complicated and often involve many actors, including citizens, governments, and organizations. Organizations frequently collaborate to tackle collective action problems related to environmental management. Here, we study two such networks collected as part of the U.S. Forest Service's Stewardship Mapping and Assessment (STEW-MAP) project that monitors and maps the organizational characteristics of local environmental groups. We apply Exponential Random Graph models to demonstrate that network motifs, spatial proximity, organizational attributes, neighborhood context, and main issue focus all play different roles in explaining organizational collaboration among civic groups, but in very different ways across the two cities. Our findings reveal that civic networks are more correlated with homophily by social issues in Philadelphia, whereas civic networks in New York City are often correlated with geography proximity and homophily in land use. The comparative framework, still relatively rare in studies of environmental stewardship organizations, shows that different types of homophily, corresponding to different theoretical motivations, are at work in these cities. We conclude with some speculation as to the causes of these differences and their implications.
