A layer shows the topology projected onto a given span. By default, and as a minimum, there are two layers present: one at the hub and one at the shroud. In many cases, additional layers are required to improve mesh quality. The addition of layers improves the 3D mesh by adapting the topology to the local geometry before mesh generation. Creating (and adjusting if necessary) additional layers enhances the quality of the mesh by creating a curve for the mesh to follow between the hub and the shroud. The more complex the blade shape-change from hub to shroud, the more layers are required.