A new spectral-frequency method (SFM) for the study of solid body surfaces is briefly described. The method allows us to estimate sizes of asteroid spots of different nature. We compare and discuss the estimates for asteroid spot sizes obtained through the SFM and other methods. The sizes of spots on the surface of asteroid 1620 Geographos which are determined using the SFM are in good agreement with the crater sizes obtained from radar data. The sizes of hydrosilicate spots on the surface of asteroid 21 Lutetia which are found through the SFM agree with the crater sizes determined with the Rosetta spacecraft. The size of a blue spot on the surface of asteroid 4 Vesta which is found using the SFM is consistent with the size of the known crater on the south pole of the asteroid. We can conclude that the SFM is a promising method for the estimation of sizes of spots on asteroid surfaces.