A structure field map is typically two-dimensional, although higher dimensional versions are feasible. The axes in an SFM are the ionic sequences. For example, in oxide perovskites ABO, where A and B represent two metallic cations, the two axes are ionic radii of the A-site and B-site cations. SFMs are constructed according to the oxidation states of the constituent cations. For perovskites of the type ABO, three ways of cation pairings exist: ABO, ABO, and ABO, therefore, three different SFMs exist for each pairs of cation oxidation states.