Very few engineered parts or structures are made up of only normal surfaces. We will continue to develop the visualization process with an introduction to inclined surfaces. Recall our definition of the three principal projection planes: frontal, horizontal, and profile. An inclined surface is a surface that is perpendicular to one of the principal planes, and is at some angle with the remaining two principal planes. To describe this surface further, it will always appear as a line in one of the principal views. In the other two remaining views, it will appear as a foreshortened area. An inclined surface will not appear true size in a principal view. Following are a few examples of simple inclined surfaces and edges and how they appear in isometric and orthographic views.