Like armatures, grids create spatial divisions in the picture plane. They differ from armatures in that the composition is usually unrelated to the divisions. A few artists have used grids to accurately draw or paint a subject. But they are mainly used to transfer drawings to large canvases or panels.
Grids derived from diagonals are scalable, so their primary purpose is to transfer drawings to larger canvases or panels.
Ingres used a grid to draw the temple in The Apotheosis of Homer, below, as well as to establish the vanishing point. In paintings like this, the line between grid and armature is blurred.
In the thirteenth-century Saint Francis Altarpiece by Bonaventura Berlinghieri, below, the armature is a grid of squares. Grid armatures facilitate the inclusion of small pictures that depict important events in a person's life.