Parallel projection is the basis of figures representing on a plane.
Let α be a plane and a be a line cutting α. Let?s construct the projection of a point A on a plane α. For this purpose through the point A let?s draw a line b||α, a cross point of b and α is A?. The point A? is called the parallel projection of a point A on a plane α (it is written: A?=PαA). The plane α is called a projective plane. Multitude of all the figure F points projections on the plane α is called a figure F projection on a plane α. If F? is the figure F projection on the plane α, then it is written F?=PαF.