Reflecting city digital twins (CDTs) for sustainable urban development: Roles, challenges and directions

City Digital Twins (CDTs) are emerging as powerful tools for sustainable urban development, offering digital representations of cities that enable monitoring, analysis, and decision-making. This paper examines the roles, challenges, and future directions of CDTs in urban governance. We identify four key functional characteristics of CDTs: heterogeneous data integration, multi-system interaction, dynamic change prediction, and bi-directional interaction with physical urban operations. Building on these characteristics, we propose a comprehensive system architecture that bridges the physical, technical, and governance aspects of CDTs through seven interconnected layers. The study reveals observation of primary challenges in CDT development and proposes strategic perspectives. These findings contribute to the growing discourse on intelligent urban governance and provide practical insights for CDTs implementation.