Plans are a set of two-dimensional diagrams or drawings used to describe a place or object, or to communicate building or fabrication instructions. Usually plans are drawn or printed on paper, but they can take the form of a digital file. Plans are often for technical purposes such as architecture, engineering, or planning. Their purpose in these disciplines is to accurately and unambiguously capture all the geometric features of a site, building, product or component. Plans can also be for presentation or orientation purposes, and as such are often less detailed versions of the former. The end goal of plans is either to portray an existing place or object, or to convey enough information to allow a builder or manufacturer to realize a design.

The term plan may casually be used to refer to a single view, sheet, or drawing in a set of plans. More accurately, plan refers to an orthographic projection looking down on the object, such as in a plan view, floor plan or bird's-eye view.

The process of producing plans, and the skill of producing them, is often referred to as technical drawing.

Format

Plans are often prepared in a set. The set includes all the information required for the purpose of the set, and may exclude views or projections which are unneccessary. A set of plans can be on standard office-sized paper or on large sheets. It can be stapled, folded or rolled as required. A set of plans can also take the form of a digital file in a proprietary format such as DWG or an exchange file format such as DXF or PDF.

Plans are often referred to as "blueprints" or "bluelines". However, the terms are rapidly becoming an anachronism, since most copies of plans that were formerly made using a chemical-printing process that yielded graphics on blue-colored paper or, alternatively, of blue-lines on white paper, have been superseded by more modern reproduction processes that yield black or multicolour lines on white paper.

Scale

Plans are usually scale drawings, meaning that the plans are drawn at specific ratio relative to the actual size of the place or object. Various scales may be used for different drawings in a set. For example, a floor plan may be drawn at 1:50 (or 1/4"=1'-0") whereas a detailed view may be drawn at 1:25 (or 1/2"=1'-0"). Site plans are often drawn at 1:200 or 1:100.

Views and Projections

Because plans represent three-dimensional objects on a two-dimentional plane, the use of views or projections is crucial to the legibility of plans. Each projection is achieved by assuming a vantage point from which to see the place or object, and a type of projection. These projection types are:

Blueprint

A blueprint is a type of paper-based reproduction usually of a technical drawing documenting architecture or an engineering design. More generally, the term "blueprint" has come to be used to refer to any detailed plan.

The term "blueprint" was originally derived from the visual aspects of prints made using the contact printing process of cyanotype. It is cyanotype which produces the white lines on blue background which are characteristic of the traditional blueprint.

For almost a century blueprint was the only low cost process available for copying drawings. Once invented no technical development was required, the process was put to widespread use immediately, notably in shipbuilding and manufacture of locomotives and rolling stock for railways. Civil engineering providing steel framed buildings and steel bridges adopted blueprint and all engineering adopted the technology.

The coated material ready for use has a shelf life of two days. Every industrial area had one or two small independent suppliers who made blueprint coated materials to order. These suppliers also provided a copying service for small users.

The normal use was to have a wooden frame with a spring loaded back, similar to a picture frame with a glass front. The drawing would be traced in indian ink on tracing paper or tracing cloth. Indoors, coated paper and tracing would be loaded into the frame which was then brought out to sunlight. Exposure time varied from less than a minute to about an hour under an overcast sky. The operator could see the blue image appear through the tracing, when ready the frame was brought indoors. The material was then washed in running water to remove the unexposed coating, then dried. It gave a clearly legible copy of the drawing with a white line and dark blue background. This copy possessed unlimited resistance to light and resistance to water that was as good as the substrate.

The diazo document copying process progressively took over from blueprint during the period 1935 to 1950.

Replacements for blueprints

Traditional blueprints have largely been replaced by more modern, less expensive printing methods and digital displays. In the early 1940s, cyanotype blueprint began to be supplanted by diazo prints or whiteprints, which have blue lines on a white background; thus these drawings are also called blue-lines or bluelines. Other comparable dye-based prints are known as black lines.

Diazo prints remain in use in some applications but in many cases have been replaced by Xerographic print processes similar to standard copy machine technology using toner on bond paper. More recently, designs created using Computer-Aided Design techniques may be transferred as a digital file directly to a computer printer or plotter; in some applications paper is avoided altogether and work and analysis is done directly from digital displays.

As print and display technology has advanced, the traditional term "blueprint" has continued to be used informally to refer to each type of image.

Floor plan

A floor plan (floorplan) in architecture and building engineering is a diagram, usually to scale (generally 1:48 or 1:96), of the relationships between rooms, spaces and other physical features at one level of a structure.

Similar to a map the orientation of the view is downward from above, but unlike a conventional map, a plan is understood to be drawn at a particular vertical position (commonly at about mid-level between floors). Objects below this level are seen, objects at this level are shown 'cut' in plan-section, and objects above this vertical position within the structure are omitted or shown dashed. Plan view or "planform" is defined as a vertical orthographic projection of an object on a horizontal plane, like a map.

The term may be used in general to describe any drawing showing the physical layout of objects. For example, it may denote the arrangement of the displayed objects at an exhibition, or the arrangement of exhibitor booths at a convention. Now drawings are reproduced using plotters and large format xerographic copiers.

It is also called a "plan" in architectural terms, as opposed to "elevation" which means how the object will look when seen from a side, or a "cross section" where the building is shown cut along an axis to reveal the interior.

A "reflected ceiling plan" shows a view of the room as if looking from above, through the ceiling, at a mirror installed one foot below the ceiling level, which shows the reflected image of the ceiling above. This convention maintains the same orientation of the floor and ceilings plans - looking down from above. Reflected Ceiling Plans or RCP's are used by designers and architects to demonstrate lighting, visible mechanical features, and ceiling forms as part of the documents provided for construction.