Initially an embedding module (22) determines an embedding of a lattice in a two-dimensional plane. The embedding module (22) then processes the initial embedding to generate a planar graph in which no links cross. The planar graph is then simplified by a link encoding module (24) and data representing the lattice structure is generated by a shape encoding module (26)--in which the simplified planar graph is represented by a shape encoding (42) identifying the numbers of links bounding areas defined by the planar graph and data identifying the locations of those areas within the planar graph; and a link list (43) identifying the modifications made to the lattice structure by the link encoding module (24). These encodings are such that the same substructures within a lattice are represented using the same data and hence are suitable for compression using conventional techniques.