Drawing 2D Sprites - Learning Windows 8 Game Development - page 39

A cube in perspective (left) and orthographic (right) projections
The problem with using the perspective projection for 2D is that we may want our
sprites to look 3D, but they contain no depth information. When rendered with sprites
sitting behind them, they will look mismatched and wrong. This is where the Ortho-
graphic projection comes into play. An orthographic projection prevents perspective
from entering the image and allows us to control the illusion of the depth in a way
that fits with the 2D sprites we are using.