We present a statistical analysis, based on a systematic clustering method, of a data set integrating the global abundances maps of iron, titanium, and thorium derived from Clementine and Lunar Prospector. Homogeneous geological units are compositionally characterized and spatially defined in relation to the major rock types sampled on the Moon. With the lowest abundances in Fe, Ti, and Th found on the Moon, the lunar highlands terrains are quite homogeneous with two major large feldspathic units, one being slightly more mafic than the other. Two distinct regions with unique compositions are unambiguously identified: the Procellarum KREEP Terrane (PKT) and the South Pole--Aitken (SPA). The PKT, which includes all the units with Th abundances higher than 3.5 ppm (KREEP-rich materials), is delimited by an almost continuous ring-like unit. In particular, it includes the western nearside maria, except for Mare Humorum. Within the PKT a Th-rich unit, corresponding to the highest Th concentrations found on the Moon, may represent KREEP volcanic deposits excavated from relatively shallow depth. With concentrations in Fe, Ti, and Th enhanced relative to the surrounding highlands, the South Pole--Aitken basin floor represents a large mafic anomaly on the farside, suggesting wide deposits of lower crust and possible mantle materials. However, due to indirect residual latitude effects in the Clementine spectral reflectance measurements, iron abundances might have been overestimated in SPA, thus implying that crustal materials, rather than mantle materials, might represent the dominant contributor to the mafic component exposed on the basin floor.