Mappe generative: dalla legibilità all'istituzione del sottosuolo come luogo urbano

The paper investigates how the diagrammatic map of the metropolitan network, exemplified by Harry Beck’s 1933 proposal, has functioned as a navigational aid and a creative device capable of constituting the underground as an urban place. The aim is to demonstrate that creativity, in this case, does not coincide with artistic origi nality, but rather with a situated technique that produces material and institutional effects: through graphic constraints (standardized angles, linearity, codified chromat ic schemes), typographic rules, and selective emphases (nodes, interchanges, anchor ing to the river), the diagram rewrites spatial hierarchies, detaching representation from geographical fidelity in order to maximize functional legibility. The hypothesis advanced is that this visual grammar does not merely describe a pre-existing infra structure, but establishes conventions, enables routines, renders paths practicable, and, in so doing, transforms the underground from a non-place into a regulated and shared place. Methodologically, the paper combines a historical reading of the cartographic trans formations of the network with a semiotic analysis of the diagram and a theoretical framework that intertwines conceived, perceived, and lived space. This framework clarifies how standardisation and abstraction produce cognitive linkages between depth and surface, aligning everyday practices, signage, and the urban imaginary. The findings highlight three complementary outcomes: the institution of a reproducible graphic syntax that renders the underground recognisable, navigable, and narratable; the establishment of a generative platform capable of guiding network extensions, inter-city translations, and design reuses over time; and the intrinsic ambivalences of this normative power, which magnifies centres, compresses peripheries, and reduces local detail while nonetheless offering operational clarity. In conclusion, the network map operates as an act of infrastructural creativity: it does not add ornament, but institutes forms of use and governance of flows, repositioning the relationship between representation and the city. This shift, sustained by formal constraints and a shared graphic lexicon, suggests that the diagram should not be regarded merely as a support for mobility, but as an urban-defining instrument that renders the subterranean an integral component of metropolitan experience and order.