The stereographic net is a tool that simplifies the construction of a stereogram. The nets we have so far used (p. 18) are equatorial nets; they can be thought of as the stereogram of a whole set of tilted planes (or protractors), hinged about a line in the plane of projection (Fig. 9b). This design of net is ideally suited for plotting great circles of dipping planes, or for plotting the pitch of lines within such dipping planes.

The plotting of lines described by means of their angles of plunge can also be carried out using the same type of net (pp. 22–3). The angle of plunge of any line is defined with respect to a vertical plane passing through that line (see p. 8). As a result, only the two (straight) great circles can be used to count out plunge angles. This means that the net needs to be rotated to allow the plotting of a line with a specific direction of plunge.

On the other hand, the use of a net with a different layout, the polar net, makes it unnecessary to rotate the the net during the procedure for plotting plunging lines (including plane normals). This net can again be thought of as a suite of planar protractors, but now all vertical and with differing strikes (Fig. 21a). The great circles of the polar net are straight lines and radiate from the centre; small circles are concentric about the centre (Fig. 21c, 21d).