1. A process for designing a rugged pattern on a golf ball surface, the process comprising the steps of: (1) creating a phantom sphere corresponding to the golf ball surface of a golf ball; (2) assuming a large number of circles on a surface of the phantom sphere; (3) assuming a large number of generating points based on positions of the large number of circles; (4) assuming a large number of Voronoi regions on the surface of the phantom sphere by a Voronoi tessellation based on the large number of generating points; and (5) assigning a dimple and a land to the surface of the phantom sphere based on contours of the large number of Voronoi regions; and (6) making a rugged pattern including dimples and lands on the golf ball surface based on the assigned dimple and land on the surface of the phantom sphere, wherein, at the step (2), a large number of circles whose diameters are equal to or greater than 2.0 mm but equal to or less than 6.0 mm are assumed.