This paper introduces the Spatially Extended Anchoring Mechanism (SEAM) as a 3-D user-interface metaphor to connect virtual worlds and manage scalability in distributed virtual environments. SEAMs provide a visual and navigable connection between worlds to manage both the complexity of rendering and network communication typically occurring in such environments. In the context of augmented reality, SEAMs can be applied as a 3-D window interface. A rendering algorithm is described which performs well on the graphics accelerators of standard personal computers.