The localization properties of the valence electronic density are considered for superheavy atoms in the range of atomic numbers 112 ≤ Z ≤ 120, paying special attention to oganesson atom (Z = 118). As in [P. Jerabek et al., Phys. Rev. Lett. 120, (2018) 053001], the atomic shell structure is studied by means of the relativistic calculations using a non-relativistic expression for electron localization function. The influence of the relativistic effects on the distribution of the valence electronic density is evaluated by performing related calculations in the non-relativistic limit. One-electron Dirac-Fock and Hartree-Fock valence subshell densities are calculated and no signs of smearing out these densities are found.