Abstract Slope Mass Rating (SMR) is a widely used rock mass classification intended to characterize and classify rocky slopes. It is based on basic Rock Mass Rating (RMRb), and is obtained by subtracting a factorial correction factor depending on the discontinuity and the slope face geometrical relationship (F1×F2×F3), and adding a correction factor depending on the excavation method (F4). Originally, SMR classification was established empirically from the study of twenty-eight slopes affected by different degrees of instability. As a consequence, an analysis of SMR classification seems to be necessary in order to better understand the performance of this rock mass classification. In this paper, a four-dimensional visual analysis of SMR geomechanical classification by means of the Worlds within Worlds methodology is performed in order to explore, analyze and visualize the relationship among the main controlling parameters of this geomechanical classification. The study reveals that several cases exist where the slope-discontinuity geometrical relationship scarcely affects slope stability, and as a consequence SMR can be computed by correcting basic RMR only with the F4 factor.