Therefore, any point P of the pre-image has as an image, through a projection t on a set of points E based on the pencil of parallel lines to a line D, the point of intersection of E with the parallel to D that passes through point P. And any point P of the pre-image has as an image, through a projection t on a set of points E based on a pencil of lines with centre c, the point of intersection of E with the line that passes through the point P and the centre c.

The idea of projecting a figure means "launching forward". We can project a solid on a plane, like in the case of the different models of projecting the Earth’s surface (a sphere) onto a flat surface to make maps. The study of projections on a line in a plane or on a plane in space falls under descriptive geometry and projective geometry. Here is a diagram of some types of projections that can be used in primary or secondary school teaching: