Defining appropriate boundaries for planning and management purposes has always been tricky. Regional boundaries are usually defined by the variables under study (e.g. vegetation, soils, transport) and sometimes by external factors, such as the availability of data or political jurisdictions, which may configure boundaries (Tiebout 1964). US planning scholar John Friedmann (1964) has shown how economic development transcends boundaries, and how different regional boundaries are necessary at different stages of development, to achieve efficient planning. When the region is ill-defined though, planning may not achieve its goals (Friedmann 1964; Simmonds 1997). Are there unique kinds of regional boundaries that environmental planners need to define and manage? How does this affect planning practice?