## 2 Background and Definition of CIM
### Definition of CIM  
The conceptualization of CIM traces its origins to 2007, a period when the concept was in its nascent stages, and the interpretations of CIM were relatively uniform. [PERSON] [36] initially framed CIM as an extension of BIM, applying BIM principles to a broader urban context. This foundational perspective primarily positioned CIM as an urban-scale adaptation of BIM. Subsequent definitions have introduced greater nuance and depth. [PERSON], in a CIM interview, proposed three distinct levels of CIM, namely ontological CIM, narrow CIM, and broad CIM, spanning from foundational data management to specialized application platforms. [PERSON] [37] expanded this understanding by emphasizing CIM's role in future-oriented urban development and human-city interaction, particularly its capacity for predictive analysis, decision support, and the facilitation of intelligent, human-centric urban growth. [PERSON] [38] proposed a novel integration of BIM into a GIS, conceptualizing CIM as a framework to enhance the semantic attribution of 3D digital city models, thereby improving the urban construction and management practices. [PERSON] [39; 40; 41] further defined CIM as an idealization of a 3D GIS, drawing an analogy to BIM but extending its applicability to the scale of cities. [PERSON] [42] advanced the discourse by advocating for the integration of a city information model based on an open data schema, specifically designed to estimate the inundation damage to city facilities. This approach emphasizes the importance of comprehensiveness, interoperability, extensibility, and usability in CIM frameworks. By systematically categorizing these definitions, a more nuanced comprehension of the pivotal role and extensive applications of CIM in the contemporary urban planning and management is achieved. CIM transcends its identity as a mere technological platform; it represents a holistic, data-driven paradigm for urban management, designed to address the inherent complexity and dynamic demands of modern cities, thereby fostering intelligent and sustainable urban development [15; 38; 43]. The contemporary conceptualization of CIM embodies a digital city modeling framework that integrates advanced technologies such as BIM and GISs, with the overarching objective of providing full lifecycle support for urban planning, design, construction, and management. Through the adoption of CIM, city managers are empowered to access more comprehensive urban datasets, facilitate cross-departmental collaboration, and enable data-driven, intelligent decision making. These capabilities ultimately contribute to enhancing urban sustainability and elevating the quality of life for residents [29]. As CIM evolves, international standards play a key role in its global adoption. The ISO 19650 standard, for example, offers a comprehensive framework for building information management, focusing on the organization, digitization, and management of information throughout the asset life cycle, ensuring interoperability and sustainability in urban development [44]. Additionally, standards like ISO/IEC 30162:2022 and ISO/IEC 30173:2023, which address the IoT and digital twin technologies, are closely related to CIM [45; 46]. ISO/IEC 30162:2022 ensures IoT system compatibility, facilitating seamless data sharing, a key aspect of CIM functionality [45]. ISO/IEC 30173:2023 establishes the terminology for digital twin systems, enhancing the real-time monitoring and decision making in CIM [46]. Furthermore, standards such as ISO 37120 and ISO 37106 focus on smart cities and sustainable urban development, providing essential guidelines for data sharing, system interoperability, and resilience [47; 48]. These standards collectively advance CIM practices, supporting cities in adapting to new challenges and technologies. Key milestones in CIM standard development and their impact on implementation are summarized in Table 1.