An Overview of Architectural Drawings
Here, we present a broad overview of architectural drawings, organized by the type of graphic projection each employs.
Architectural Graphic Projection
Architectural drawing is as old as the discipline itself. By some accounts, it was the formalization of architectural drawings that established architecture as a discipline distinct from the building trades. For most of its history, architectural drawing has relied heavily on techniques of graphical projection, understood as protocols by which images of three-dimensional objects are projected onto a planar surface. Some form of graphical projection (typically parallel projection, orthographic projection, or perspectival projection) - either performed by hand or automatically generated with the aid of a computer - are employed on the vast majority of architectural drawings.
The diagram and videos below describe the four types of graphic projection most commonly used in architectural practice. Note the changing relationship between the object depicted, the draw plane (sometimes called the "projection plane", "cut plane", or "section plane"), and the projection rays. While some of the terms below are often used casually in practice, understanding the precise definitions can draw some helpful distinctions:
Distinctions Among Parallel Projections
- Orthographic projections
- Projection rays are parallel to one another, and perpendicular to both the image plane and a dominant plane of the object depicted.
- Axonometric projections
- Projection rays are parallel to one another, and perpendicular to the image plane - but in no specific relationship to any dominant plane of the object depicted.
- Oblique projections
- Projection rays are parallel to one another - but non-parallel with the image plane and in no specific relationship to any dominant plane of the object depicted.
Parallel vs Perspective Projections
- Parallel projections
- Projection rays are parallel to one another. Includes all drawing types listed above.
- Perspective projections
- Projection rays are converge at a "station point" representing the disembodied eye of a viewer. Includes 1, 2, 3, and 4 point perspectives.
Introductory Videos on Graphic Projection
A basic introduction to the principles of orthographic projection.
Axons and Obliques
A discussion of the construction of axonometric and oblique projection drawings, and how these are distinguished.
The geometric principles behind perspective projections.
- The Theory and Practice of Perspective
- A 1910 instruction manual for drawing in perspective, by George Adolphus Storey.
There are a couple of workflows that document the geometric construction of perspective drawings given a plan and elevation using the "office" method
- One-Point Perspectives
- Construction of one-point perspectives using the office method.
- Two-Point Perspectives
- Construction of two-point perspectives using the office method.
Conventions of Line Weight and Type
In the general application of graphic projection drawing (not looking at architectural drawing in particular), there exist two models for the application of line weight to drawings produced by graphic projection - one that differentiates lines by distance from the projection plane, and another that differentiates lines by their role in depicting spatial relationships.
Differentiation by Distance
Differentiation by Spatial Relation
Common Uses of Graphic Projection in Architecture
A plan is an orthographic projection representing a horizontal cut through an object or building. By convention, a plan is taken relative to an occupiable space or walking surface such that the "cut plane" of the plan is positioned 4' above this surface. This convention may be broken in certain cases, such as depicting a sloped floor or in order to depict the visual experience of a space with more fidelity. In more rare cases, the cut plane of plans may sometimes be "broken" or "jogged" in order to illustrate a specific architectural idea.
In a conventional plan, lines depicting object further away from the cut plane are drawn progressively thinner, following the conventions of drawing in elevation. Objects above or behind the cut plane are dashed.
A section is an orthographic projection representing a vertical cut through an object or building and help illustrate spatial qualities within a space.
Where to cut a section is up to you – it is important to cut in areas that demonstrate the BEST and most INTERESTING spaces within the building. Typically, you could not cut through an elevator or stairwell. Auditoriums or light-wells make for good section cuts. Similar to plans, the cut line is the darkest line.
Technically a type of section, an elevation is an orthographic projection representing a vertical view of the outside of a building, looking back at the face. Elevations are typically used to illustrate how the building will look from the outside.
Like all orthograpic projections, an elevation employs a drawing plane (or "cut plane") plane. Since this plane is positioned such that it does not intersect the building in question, no section cut of the building is drawn. However, it is important to note that, when drawing a building on site that the site itself, including any adjacent buildings or topography, must be represented in section when drawing an elevation.
An architectural axonometric is subset of orthographic projection, and includes any drawing wherein the projection plane is positioned at a non-perpendicular angle relative to the ground or the object depicted.
An architectural perspective is a subset of planar projection drawings wherein lines of projection begin with objects in the scene and converge at an imaginary "station point" that stands in for an observer's eye. Where these rays intersect a projection plane, an image is inscribed that approximates an image of the scene as it would be seen by the eye. This protocol is in contrast to orthographic projection drawings, wherein the lines of projection are parallel with each other, and perpendicular to the projection plane.
Scales and Drawing Formats
Architectural documents are drawn at a specific ratio relative to the actual size of the designed work.
There are a number of competing standards for architectural paper sizes and formats.
Cut Lines and Poche
Lines that depict the intersection of an object with the cut plane of the plan hold the darkest line weight (typically an HB or B lead). When depicting solid objects, these cut lines will always form enclosed regions in the projected drawing. Always. These enclosed regions are called the "poché" of the drawing - there exist a number of styles for depicting these cuts.
Line Weight, Style, and Type
The "weight" of a line simply refers to the thickness (or sometimes darkness) to which a line is rendered graphically. This basic graphic property has enormous effect upon how a drawing is perceived, and how the illusion of three-dimensional space is produced through two-dimensional drawings. Similarly, a range of line types (dashed, dotted, etc) may be deployed in different situations to produce a range of effects.