This creates visual “checkpoints” that the viewers’ eyes can land on, from these checkpoints, the eyes are led down the spiral to its endpoint at the large dark shadow on the left side of the scape.
Notice how the hardscape and aquatic plants near the highlighted red sections of this scape guide your eyes along the spiral. This creates visual “checkpoints” that the viewers’ eyes can land on, from these checkpoints, the eyes are led down the spiral to its endpoint at the large dark shadow on the left side of the scape.