Isometric perspective, also called isometric projection, is a specific way of representing a three-dimensional image in two dimensions. The word "isometric" indicates "equal measure." In isometric projection, the three axes are separated from each other by equal angles and parallel lines remain at an equal distance from each other.
In isometric drawings, there are 120 degrees between any two of the three axes. This means a cube represented in isometric projection is drawn as three equal parallelograms. Vertical lines in the original object remain vertical in isometric projection, while the edges of horizontal planes are drawn 30 degrees above the horizontal. Isometric perspective preserves the relative proportions of 3D objects, unlike regular perspective drawings where nearer objects appear larger than more distant objects.
Technically speaking, isometric projection is not perspective drawing because objects do not get smaller with distance. This makes isometric projection valuable for technical drawing since it preserves proportions. There are relatively straightforward matrix transformations that can calculate the projection of a 3D object from any of the eight possible isometric projections, which can be visualized as looking down on any of the eight corners of a cube. The relative simplicity of isometric representations makes it a popular projection in some computer games and comics.
While isometric perspective preserves the proportional distances between parallel lines in all three dimensions, it does create minor distortion in the diagonals. There is also some information lost in an isometric projection, making it impossible to judge certain distances. This effect is the key behind the Penrose stairs, a famous optical illusion in which a loop of stairs seems to ascend endlessly. Using several images that portray the same object from different angles can help solve this problem.
Since isometric projection keeps the relative proportions of an object equal in all three axes, it is commonly used in technical and architectural drawings to allow measurements on the drawing to accurately reflect the measurements of the actual object or building. Overhead isometric perspective is also used in many computer games. It requires no more than four sprites to represent any game object and allows player characters to travel any distance without requiring the perspective to change.