Chapter 5 - Inclined Surfaces in Orthographic Projections

Example 5-4

In the views where the inclined surface appears as an area, the shape of the area must be similar. For example, if the shape of the inclined surface is defined by six points, the foreshortened views of that surface must also have six points.
It is easy to simulate this to convince yourself. Draw a moderately complex shape on a sheet of paper. If you hold the paper so your lines of sight are perpendicular to the sheet, you will see the true size of the shape. Now turn the sheet so your line of sight is no longer perpendicular to the sheet. You will see a foreshortened view of the surface. As you continue to turn the page, you will see that the shape of the area is similar. Eventually you will see the edge view of the surface.