The growing designation of historic landscapes and structural ensembles across the United States highlights the increasing emphasis on heritage preservation. A significant component of this movement is the establishment of historic districts—defined areas that hold substantial historical and cultural value. Unlike the conservation of single buildings, landmark districts emphasize the collective importance of groups of structures and their surrounding landscapes or cityscapes. Central to the identity and preservation of these districts are their edges, which often remain an under-examined element. The delineation of historic district boundaries plays a crucial role in maintaining the district’s historical atmosphere, acting both as a protective buffer and as a means of contextual continuity. Understanding the basis for defining these edges and their implications is vital for effective preservation planning and for controlling the surrounding environment of such districts.