Plan view

In technical drawing and computer graphics, a multiview orthographic projection is a technique of illustration by which a standardized series of 2-dimensional pictures is constructed to represent the form of a 3-dimensional object.

To render each such picture, a ray of sight towards the object is chosen, which determines on the object various points of interest (for instance, the points that are visible when looking at the object along the ray of sight); those points of interest are mapped by an orthographic projection to points on some geometric plane that is perpendicular to the ray of sight, thereby creating a 2D representation of the 3D object.

Customarily, 2 rays of sight are chosen for each of the 3 axes of the object's coordinate system; that is, parallel to each axis, the object may be viewed in one of 2 opposite directions, making for a total of 6 orthographic projections (or "views") of the object:

These 6 planes of projection intersect each other, forming a box around the object, the most uniform construction of which is a cube; traditionally, these 6 views are presented together by first projecting the 3D object onto the 2D faces of a cube, and then "unfolding" the faces of the cube such that all of them are contained within the same plane (namely, the plane of the medium on which all of the images will be presented together, such as a piece of paper, or a computer monitor, etc.). However, even if the faces of the box are unfolded in one standardized way, there is ambiguity as to which projection is being displayed by a particular face; the cube has 2 faces that are perpendicular to a ray of sight, and the points of interest may be projected onto either one of them, a choice which has resulted in 2 predominant standards of projection:

Orthographic projections show the primary views of an object, each viewed in a direction parallel to one of the main coordinate axes. These primary views are called plans and elevations. Sometimes they are shown as if the object has been cut across or sectioned to expose the interior: these views are called sections.

Auxiliary views are sometimes taken from an angle that is not one of the primary views but these are not orthographic projections.

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Wikipedia