All the two-dimensional structures of adatoms are presented on a surface lattice including higher-order commensurate structures systematically, using a four-dimensional parameter space, as long as the adatoms do not have a fine structure in a basis cell of a Bravais lattice. In this method, commensurate structures of an Li adsorbed system on an Ni(001) surface are investigated. A 'ladder' structure is found to be stable when the substrate potential is strong.