The usefulness of the stereographic projection for solving problems in structural geology can be most easily demonstrated with reference to the real structures shown in Figure 5.

Figure 5a shows folded beds of sandstone exposed on the coast at West Angle, near Pembroke, Dyfed, Wales. The orientations of bedding planes (planar structures of sedimentary origin) are being measured at a none of locations at the site.

Figure 5b shows a geology student taking one of these measurements. He is in fact measuring the strike line on one of the dipping bedding surfaces. These measurements are being recorded in a field notebook using the strike/dip/dip direction convention described on p. 4. Figure 5c shows an extract from his notebook.

The measurements of the orientation of the bedding planes are also being recorded on a large-scale map (Fig. 5d). The symbols on the map show that the strike of the bedding planes changes in an orderly way, as expected from the fact that the bedding planes have been folded. The angles of dip also vary from one part of the site to another in a systematic way.

To be able to interpret these orientation data efficiently we need some convenient form of display or graph which brings out the pattern of variation of bedding attitudes. A circular histogram (or rose diagram) like the one in Figure 5e could possibly be used to show the variation of strike directions, though a separate histogram like that in Figure 5f would be required to examine the variation in the angles of dip.