Ivan Sutherland's Sketchpad (1963) showed that drawings could be geometric objects with constraints rather than ink on paper. Cheap microcomputer CAD — AutoCAD from 1982 — replaced the drawing board within a decade, making plans infinitely editable, layered, copyable and dimensionally exact. Object-based modelling followed: Graphisoft's ArchiCAD (1984) and Revit (2000) represent buildings as parametric components carrying data, which as building information modelling became a coordination and procurement platform, mandated for public projects in the UK from 2016 and elsewhere. Coupled to GIS, these models scale up to city-level digital twins.
CAD and BIM changed the medium of planning and so its products: rapid variant testing, exact quantity take-off, clash detection and the copy-paste repetition visible in globalised commercial architecture. Digital models are now the legal and contractual object of a project, shifting authority towards whoever controls the model and its standards. They also make automated checking of zoning, daylight and code compliance feasible, quietly moving regulation into software.
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