From urban modelling to city digital twins – Reflections from the applied urban modelling (AUM) symposia

City digital twins (CDTs), as digital replica of urban systems and development processes, have been heralded as the next-generation technology for urban planning and management. Arguably, the concept of CDTs is not new. Prior to CDTs, applied urban modelling has been playing a pivot role in supporting city and infrastructure planning since the 1960s. Examining CDTs in relation to conventional urban models can thus offer valuable insights into their nature, potential, and challenges. Such a comparative, reflective exercise, however, remains rare. This commentary aims to share insights and reflections from a dedicated applied urban modelling (AUM) community. It is argued that to substantiate the power of CDTs, a theory-driven modelling strategy is essential for both practical policy analysis and knowledge discovery. Modellers must think beyond the technical perspective and exploring novel use of CDTs beyond optimisation. A blind pursuit for data without building on and expanding existing domain knowledge remains an existential risk for CDTs.