Hierarchical Integration Framework for Urban Digital Twins: A Technical Path from Concept to Practice

This article introduces a doctoral study on data integration for Urban Digital Twins (UDT), proposing a three-level integration framework (model layer, database layer, frontend layer) and developing the open standard-based City2Twin platform. It provides practical guidance for data integration and interoperability in smart cities, helping UDT move from concept to practice.

Urban Digital Twins (UDT) are reshaping urban planning and decision-making, but they lack clear definitions and shared technical foundations. The core challenge is the fragmentation in integrating heterogeneous data (3D models, BIM, IoT, etc.). Different solutions have varying mechanisms and limited interoperability, forming "data silos" that cause difficulties at all stages of the UDT lifecycle.

The researchers propose a three-level integration framework:

1. Model layer integration: Unify conceptual models through schema extension to flexibly adapt to new data requirements;
2. Database layer integration: Adjust the underlying database structure to align with the target model, enabling tight coupling and efficient queries;
3. Frontend layer integration: Unify the display of data from different sources at the visualization level, which is lightweight but may affect consistency and real-time performance.

The City2Twin platform was developed based on open standards (e.g., CityJSON) and Web architecture, featuring flexibility (supports multiple data formats), interoperability (compatible with open standards), and maintainability (modular architecture). After testing with multiple use cases (integration of BIM, IoT, and simulation data), it was found that the choice of integration method needs to be based on application context, data characteristics, and lifecycle requirements.

The study reveals:

1. There is a gap between theoretical definitions and actual development; UDT is still in the exploration stage;
2. Integration methods require trade-offs: the model layer is flexible but may sacrifice performance, the database layer has tight coupling but high maintenance costs, and the frontend layer is simple but has limited functionality;
3. Successful implementation requires a systematic methodology, and this study lays the foundation for the development of the UDT ecosystem.

For planners and developers: The three-level framework helps select appropriate technical paths and avoid pitfalls; the open-source implementation of City2Twin lowers the entry barrier, making it suitable for small and medium-sized cities and teams. As smart city initiatives advance, lightweight and standardized methods are expected to be widely adopted, promoting the large-scale implementation of UDT.