City Information Modelling and Urban Digital Twins: A Comparative Study of Imperative and Declarative Modes

Urban planning and design increasingly address systemic complexity, involving heterogeneous actors, multi-scalar interactions, and long-term uncertainty. Urban Digital Twins (UDTs) have emerged as instruments for data-driven urban analysis and decision support, yet their relationship to City Information Modelling (CIM) remains insufficiently articulated. This paper argues that UDTs should be understood not as self-contained technological artefacts, but as operative configurations within CIM, which provides the organisational and conceptual infrastructure for structuring urban information. To clarify this relationship, the paper introduces a distinction between imperative and declarative modes of Urban Digital Twinning. Imperative modes translate urban ambitions into indicators, thresholds, and evaluative metrics that support benchmarking, negotiation, and decision-making. Declarative modes use relational reduction strategies that preserve underlying configurations and support interpretive reasoning before evaluative closure. The argument is developed through a comparative conceptual–analytical reading of two practice-oriented applications in the Netherlands, Eindhoven and the Schiphol Area Development Corporation, and an exploratory research project centred on Graz, Austria. The comparison examines data sources, spatial units, transformation procedures, output forms, uncertainty treatment, and validation logic. The Dutch cases show how imperative UDTs support policy translation and multi-stakeholder coordination, while the Graz case demonstrates how declarative twinning can articulate structural tendencies for early-stage environmental interpretation. The paper contributes to CIM discourse by clarifying the role of UDTs within broader informational frameworks and positioning declarative twinning as a practical complement to performance-oriented approaches for engaging urban complexity beyond benchmarking alone.