Third angle projection

Figure 2.10 shows a small cornflake packet (courtesy of Kellogg's) that has been cut and folded back to produce a development of a set of six connected faces. Each one of these faces represents a true view of the original box. Each face (view) is folded out from an adjacent face (view). Folding the faces back and gluing could reassemble the packet. The development in Figure 2.10 is but one of a number of possible developments. For example, the top and bottom small faces could have been connected to (projected from) the back face (the 'bowl game' face) rather than as shown. Alternatively, the top and bottom faces could have been connected. Figure 2.11 (courtesy of Kellogg's) shows the same layout but with the views separated from each other such that it is no longer a development but a series of individual views of the faces. The various views have been labelled. The major face of the packet is the one with the title 'Corn Flakes'. This face is the important one because it is the one that would be placed facing outwards on a supermarket shelf. This view is termed the 'front view' and all the other views are projected from it. Note the obvious names of the other views. All the other five views are projected from the front face view as per the layout in Figure 2.10. This arrangement of views is called third angle orthographic projection. The reason why this is so is explained below. The third angle orthographic projection 'law' is that the view one sees from your viewing position is placed on the same side as you view it from. For example, the plan view is seen from above so it is placed above the front face because it is viewed from that direction. The right-side view is placed on the right-hand side of the front view. Similarly, the left-side view is placed to the left of the front view. In this case, the rear view is placed on the left of the left-side view but it could have also been placed to the right of the right-side view. Note that opposite views (of the packet) can only be projected from the same face because orthographic relationships must be maintained. For example, in Figure 2.11, the plan view and inverted plan view are both projected from the front view. They could just as easily have both been projected from the right-side view (say) but not one from the front face and one from the rightside view. It is doesn't matter which arrangement of views is used as long as the principle is followed that you place what you see at the position from which you are looking. 
Engineering Drawing for Manufacture
by Brian Griffiths
Publisher: Elsevier Science & Technology Books