Over more than two centuries, the grid street system introduced by the 1811 Commissioners’ Plan has retained its fundamental structure while gradually transforming through insertion of passages, plazas, and facilities. This study conceptualizes this grid as the city’s “primary structure” and defines inserted passage and public spaces as“secondary structures.”It genealogically traces grid transformation caused by these insertions, using institutional triggers and spatial configurations. Particular attention is given to mid-block trails as a supplementary pedestrian passage within the grid that emerged through this process. Their formation is categorized and discussed within four genealogical stages:“Germ,”“Emergence,”“Development,” and “Generalization.”
Mizuma et al. (Tue,) studied this question.