Next, just like in our organic forms with contour curves, and even in our dissections, we add contour lines to give the form volume and form.
Note: You may notice that these contour lines are a little different from what we used in the previous contour line exercise - but in fact, they're essentially the same. Contour lines run along the surface of a given form, and in doing so, they describe how that form turns in space. In the previous exercise, we focused on contour lines that run perpendicular to the flow of our sausage form, but we can run them in whatever direction we like - though some are more effective than others.
As you complete this step, think about what it is you're doing - you're not just drawing lines on a page. You're imbuing a flat shape with volume, with weight, with solid form. It's no longer just a 2D shape, but a 3D object that can be lifted, moved, thrown and dropped. If you pick it up from one end, it will dangle. If you hold it from its middle, it will sag on both sides.
Don't move ahead until you can feel it in your mind, that this form has real weight to it.