text: The reciprocal lattice is easily constructed in one dimension: for particles on a line with a period , the reciprocal lattice is an infinite array of points with spacing . In two dimensions, there are only five Bravais lattices.  The corresponding reciprocal lattices have the same symmetry as the direct lattice.  2-D lattices are excellent for demonstrating simple diffraction geometry on a flat screen, as below. 
  Equations (1)–(7) for structure factor  apply with a scattering vector of limited dimensionality and a crystallographic structure factor can be defined in 2-D as .
  However, recall that real 2-D crystals such as graphene exist in 3-D. The reciprocal lattice of a 2-D hexagonal sheet that exists in 3-D space in the  plane  is a hexagonal array of lines parallel to the  or  axis that extend to  and intersect any plane of constant  in a hexagonal array of points.
  The Figure shows the construction of one vector of a 2-D reciprocal lattice and its relation to a scattering experiment.
  A parallel beam, with wave vector  is incident on a square lattice of parameter . The scattered wave is detected at a certain angle, which defines the wave vector of the outgoing beam,  (under the assumption of elastic scattering, ). One can equally define the scattering vector  and construct the harmonic pattern . In the depicted example, the spacing of this pattern coincides to the distance between particle rows: , so that contributions to the scattering from all particles are in phase (constructive interference). Thus, the total signal in direction  is strong, and  belongs to the reciprocal lattice. It is easily shown that this configuration fulfills Bragg's law.