Correlation among transition temperature, in-plane Cu-O bond length, and tilt/buckling in cuprate superconductors were examined in detail. As for cuprates with a single CuO_2 layer, tilt structure was observed in the region, whose in-plane Cu-O length was 1.906-1.926 Å, and that the tilt structure drastically suppressed superconductivity. As for cuprates with double CuO_2 layers, all the compounds had buckling distortion in a CuO_5 pyramid. The degree of distortion was determined only by a kind of cation between the two facing CuO_5 pyramids, that is, calcium or yttrium. A higher transition temperature was obtained for a copper oxide with having larger Cu-O length and smaller buckling degree. A common feature of layered cuprates was the existence of three major classes distinguished by the cations Ba^, Sr^, and Ln^ occupying the 9-coordination sites
