A city is a temporary organisation of movements. Energy crosses buildings, water passes through infrastructures, waste changes jurisdiction and material status, memories attach themselves to streets, voices reorganise public space, and sensory events become evidence through bodies that move across them. Situated urban flow names this condition in a way that avoids the weakness of purely metaphorical organicism. Flow is material enough to be measured, social enough to be contested, perceptual enough to be experienced and mnemonic enough to persist after its original event. The city acquires form by slowing, channelling, accelerating, storing and transforming heterogeneous currents. Urban knowledge therefore depends on the ability to identify not only what exists in a place but what passes through it, what remains, what disappears and what becomes perceptible only at a particular scale.

Urban metabolism provides the clearest systemic grammar for this proposition. Material-flow analysis, life-cycle assessment, thermodynamic scaling and circular models make resource circulation legible as an organised urban condition. Yet metabolic knowledge becomes most productive when scale is treated as an epistemic variable rather than as a neutral container. Citywide totals can reveal aggregate dependencies while concealing neighbourhood inequalities; street-level mapping can disclose the distribution of heat, waste, vegetation and infrastructural access that macro indicators smooth away. Digital-twin research radicalises the same problem by asking how static flow accounts might become dynamic spatial representations interoperable with the tools of urban transformation. Representation is therefore not secondary to metabolism. The diagram, map, model and interface determine which relations can be seen together and which interventions can subsequently be imagined.