The appearances of parallel and perpendicular lines are prevalent all the time in engineering. Whether its calculating the forces in particular beam or if its the structure of a bridge itself. The correlation between parallel lines and perpendicular lines are very much apparent. Parallel lines also can be referenced when trying to put a photo up on a wall. If you want the photo to be level on that wall, then you virtually represent two lines. One being the floor, and the other being the top of the frame.