Orthographic projection is the most common parallel projection due to its simplicity. It is represented using three views; front view, side view and top view. In graphical terms, you need to draw the object in XY plane, YZ plane, and ZX plane, separately.
To draw the front view you just imagine how the object looks at front. Don’t think about slope of the object, just draw whatever it looks. Similarly, the top and side view of the object can be drawn (refer the image).
Through this projection, accurate measurement can be obtained because all the views are drawn using same scale. However, it doesn’t provide a realistic projection of a 3-D model; besides, it requires multiple views to feel the object design.
The orthographic projection can be drawn two ways, first angle projection and third angle projection. Both of them have differences only in the positioning of various views. In first angle projection, the front view is placed onto first quadrant; top and side view are placed onto the forth and second quadrants, respectively. In the third angle projection, the third quadrant is used for front view; whereas top and side view are placed onto the second and forth quadrants.