**Orthographic projection**is a means of representing a three-dimensional object in two dimensions. It uses multiple views of the object, from points of view rotated about the object's center through increments of 90 degrees. Equivalently, the views may be considered to be obtained by rotating the object about its center through increments of 90 degrees.

The views are positioned relative to each other according to either of two schemes: *first-angle* or *third-angle* projection. In each, the appearances of views may be thought of as being *projected* onto planes that form a transparent "box" around the object:

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2 Third-angle projection 3 Additional information |

## First-angle projection

A two-dimensional representation of the object is then created by "unfolding" the box, to view all of the*interior*walls:

## Third-angle projection

In **third-angle projection**, each view of the object is projected "outward" from the object, onto the (transparent) exterior walls of the box:

*exterior*walls.

## Additional information

The term "third-angle" is used because, compared to "first-angle" projection, the directions of projection are rotated through two right angles about the object. Second-angle and fourth-angle projection also are defined, but do not result in useful images.

Third-angle projection is often considered to be more intuitive than first-angle projection.