4. A system according to claim 1 , further comprising: an angle determination module to determine one or more angles from the displayed spine and to identify one of the angles as a primary angle; and an spine placement module to place the remaining cluster spine along the primary angle.
5. A system according to claim 4 , further comprising: an overlap module to determine that overlap occurs between the remaining cluster spine and the displayed spine and to move the remaining cluster spine away from the display spine along the primary angle.