2D drafting and 3D modelling

The modes differ in what is primary. In 2D drafting the drawing is the artefact: each sheet authored and maintained by hand, consistency between sheets a matter of discipline. In model-based work the 3D model is primary: coordinated in space, checked for clashes, quantified by extraction, with drawings generated as views — consistent with the model by construction, and with each other through it.

The industry's actual state is hybrid, and durably so. Contracts and authorities still consume drawings; small projects and certain disciplines still draft; brownfield work inherits 2D archives whatever the new scope uses; and the model-based project still issues sheets because the fabricator, the reviewer and the law expect them. The hybrid's tax is dual maintenance: wherever a drawing can be edited independently of the model — or survives from before the model existed — the two can diverge, and the project needs an explicit rule for which governs.

The transition between modes is not a software purchase but a data question: 2D archives become model-based information only through interpretation — of scans, of conventions, of what the draughtsman meant — which is precisely why the legacy stock persists as 2D long after the tools moved on.