A region may be divided into a set of non-overlapping areas in many ways. As we noted in Table 1‑2 a (regular or irregular) tessellation of a plane involves the subdivision of the plane into polygonal tiles that completely cover it. Within GIS regular tiles are almost always either square or rectangular, and form a (continuous) grid structure. Regular triangular and hexagonal grids are also possible in the plane but are rarely implemented in software packages. GIS does make extensive use of irregular triangular tessellations, both for division of plane regions and as an efficient means of representing surfaces.