Excerpt
Another way of measuring the model by sight is to observe the negative spaces created in a pose. Negative spaces are the empty shapes created within the outline of the pose. For example, look at the triangular shape of negative space under the model's raised leg. If you were drawing the model, and the negative space you drew resulted in a smaller area of negative space in comparison to what you observed on the model, you would know that you had erred. You can also use negative spaces when drawing strictly from your imagination. Pleasing negative spaces within a pose tend to open up a drawing.