The two-dimensional plot of a stereographic projection, in which points on the surface of a sphere are represented on a plane of projection, as points on the Earth’s surface might be projected on to a plane representing a slice through the equator by joining these points to either the N. or S. poles. If the plane of projection (equatorial plane) is constructed with great circles and small circles drawn at 2° intervals and with an overall diameter of about 20 cm, it is called a ‘Wulff stereographic net’. If it is graduated at 10° intervals and includes small circles concentric to the primitive circle and radii representing vertical great circles, it is called a ‘Federov net’. Plotting is done on a sheet of tracing paper laid over the printed net and pivoted about a pin at its centre.