It is difficult to visualize the shape of a band as a function of wavevector, as it would require a plot in four-dimensional space, "E" vs. "kx", "ky", "kz". In scientific literature it is common to see band structure plots which show the values of "E""n"(k) for values of k along straight lines connecting symmetry points, often labelled Δ, Λ, Σ, or ], respectively. Another method for visualizing band structure is to plot a constant-energy isosurface in wavevector space, showing all of the states with energy equal to a particular value. The isosurface of states with energy equal to the Fermi level is known as the Fermi surface.