1. In a computer-aided drawing system having a display and a cursor-control means for positioning a cursor on the display, a method for assisting the creation and editing of illustrations comprising the steps of: selecting a geometric mode from a set of geometric modes, at least one of the geometric modes of said set of geometric modes being adapted to facilitate drawing in two dimensions a two-dimensional representation of a three-dimensional object; displaying on said display a grid representing the selected geometric mode, the grid having an origin; placing a control point at a position on the displayed grid, said position being a point on said grid nearest to the cursor; and moving automatically the grid origin to the placed control point.