A popular way of naming what a model is used for: 3D geometry, 4D time, 5D cost, and 6D and 7D, whose meanings vary between sources and are defined by no standard.
BIM dimensions are a shorthand for what information is added to a model and what it is used for: 3D for geometry, 4D for time, 5D for cost, then 6D and 7D. The first three are used consistently across the industry. The higher numbers are not: sources disagree on what 6D and 7D mean, and no standard, ISO 19650 included, defines any of them.
The dimensions are useful in conversation and in marketing: "we do 4D" tells a client that the programme will be linked to the model. They are less useful in contracts and requirements, because "6D" can mean two different things to two parties. Information requirements should instead name the use (for example clash coordination, construction sequencing, cost planning, asset handover), the information needed for it, and when.
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