Model lines are work plane-based elements that exist in 3D space and are visible in all views. They can be drawn straight or curved, either singly or in chains, or in the shape of a rectangle, circle, ellipse, or other polygon. Because they exist in 3D space, you can use model lines to represent geometry such as cords or cables supporting a tarp.
Model lines can be drawn in the project environment, or in the massing environment.