The boundary element method can be a versatile method only if it includes the ability to represent any boundary in the given class of two-, three- or axisymmetric three-dimensional space. In general this is carried out by the facility of defining the surface as a set of panels, each having the same characteristic form (or a set of two or three characteristic forms in more advanced software). For example a closed two-dimensional boundary in two dimensions can be represented by a set of straight lines, as illustrated earlier in Figure 2.1.