**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?=P**_{α}A). 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?****=P**_{α}F.