WORKING DRAWINGS HANDBOOK, Fourth Edition

Appendix 6

describing all or part of a building, plus definitions of

any number of paper plots that might be created from

it. This was not always so. Early versions of CAD

programs could only create small files, containing just

one plotted drawing. When CAD terminology was

being coined, it wasn’t important to distinguish

between the paper plot and the computer file used to

generate it. The name stuck, hence the current

confusion.

Dyeline machine A machine used for preparing paper

prints from large drawings. Now largely superseded by

large format photocopiers. Many CAD users now create

multiple ‘originals’ rather than one original from which

copies are made.

DXF As in filename.dxf. A common file format used for

the transfer of files from one CAD system to another. All

major CAD systems can convert between their own

native file format and DXF.

DWG As in filename.dwg. AutoCAD’s file format.

Because AutoCAD is so widely used, many other CAD

programs can read and write direct to AutoCAD format,

though often with inconsistent results.

DGN As in filename.dgn. Microstation’s file format.

Microstation is another widely used CAD program.

Entities Arcs, lines, circles, text, faces and so on, held

in the drawing file, together with information about their

size, position and orientation. In dedicated architectural

design programs, walls, windows, and so on might also

be defined as ‘entities’.

Internet A communications network linking computers,

that allows people to share information. Now used

extensively to obtain information from manufacturers, to

order goods, as a means of communication by email,

and for transfer of CAD and other computer files

between professionals.

Layers May be known as ‘levels’ in some CAD

programs. A way of grouping entities together so that

their visibility can be controlled as a named set. The

CAD version of ‘Overlay Draughting’.

Model, CAD model The set of entities, objects and

other data that describe the project in full in 2D or 3D.

This is the data set from which the paper drawings are

created.

Objects Some dedicated architectural CAD programs

create their drawings from ‘intelligent objects’ rather than

entities. CAD files will be created from doors, walls and

windows rather than lines, arcs and circles. A ‘door’

object knows it is a door and interacts appropriately with

a ‘wall’ object. Move the door, say, and the adjacent light

switch moves with it. Flip the door and the light switch

moves to the other side without intervention by the

designer.

Pin registration (overlay draughting) A manual

drawing method that enjoyed popularity in a few offices

before the advent of CAD. Each type of information was

drawn on a different sheet of acetate, say walls on

one sheet, doors on a second and light fittings on a

third. Sheets were aligned by dropping the appropriate

sheets over pins fixed in the drawing board. Once the

individual sheets were finished different paper drawings

could be created by photographing the combined

image.

Printing and plotting The distinction between printing

and plotting is less important than it once was. In the

early days of CAD, the only machines capable of

producing large format architectural drawings accurately

to scale were pen and drum plotters. Printers, on the

other hand, were slow, low resolution devices, printing

mostly to A4 size.

Today, large format pen plotters have largely been

abandoned as expensive and as too troublesome to

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