The agreed plan for how a large project's model is split into separate files/volumes (by zone, floor, or discipline) so worksharing and coordination stay manageable. On a large project, one single Revit file becomes too heavy for anyone to work in efficiently, so the team agrees up front on how to split it - often by tower, floor band, or zone - and documents where each split's boundaries sit so linked models stay aligned and no scope falls between two volumes unowned.