Digital twin

A digital twin is a living virtual copy of a real thing — a building, a power grid, a whole city — kept in sync with its physical counterpart by changing data. Unlike a static 3D model, a genuine twin has a maintained relationship with the place or system it represents, so planners can inspect current conditions and rehearse changes on the copy first.

Cities build very different things under the same label. Virtual Singapore is a national planning and simulation environment; Tokyo emphasises an open 3D viewer and reusable point clouds; Seoul's S-Map adds a citywide simulation lab; and Rotterdam brings surface and subsurface infrastructure together for flood and energy planning. Our comparison of Singapore, Tokyo, Seoul and Rotterdam explains why these are four different operating models, not four copies of one product.

The caveats are steep. A twin is only as good as its update cycle, governance and source data, while maintaining thousands of models and sensor feeds is expensive and never really finished. Many products sold as twins are detailed 3D viewers with little live synchronisation. Public evidence also concentrates on technical coverage and possible use cases; independently measured improvements to planning speed, construction cost or climate resilience remain rare.