Orthographic projection refers to representing a three-dimensional object in two dimensions with multiple-view drawings. In this type of drawing, the projected lines are perpendicular (orthogonal) to the projection plane. For every three-dimensional object, there are six sides: the top, bottom and four sides. All of these views are represented in three views: top view, front view and side view of the three-dimensional object. These views are arranged in two ways: the first-angle and third-angles projections. At the completion of the drawing, special symbols are included to verify the type of projection.
Hatching is a drawing technique which employs thin lines to convey more details of the drawn figure. These lines are drawn diagonally, inclined at an angle of 45 degrees, and run parallel to each other. Hatches are mainly used in a type of drawing known as sectioning to denote where a cutting plane passes through. Also, though rarely, the hatch lines are used to show the type of material the object is made of.
Sectioning refers to the art of virtually dissecting an object along a given cutting plane and representing it on paper. The main aim of sectioning is to bring out interior details which could otherwise not be represented in orthographic drawings. Sectioning can be done by using one cutting plane or two planes if not all details are represented using one plane. The sectioned object is then drawn on paper using the same format as the one employed in the orthographic drawing.
Assembly drawing refers to the art of drawing an object having several parts as a complete unit. Usually, the components of the object are given and the engineer visualizes them and assembles them in the drawing. Upon completion, a special key called the bill of materials is indicated, showing the component's number, quantity and material types.