CAD Systems

Computer-assisted (or aided) drafting (CAD) systems are used to produce maps, diagrams, drawings, plans, and charts. CAD systems are to maps and graphics what word processing packages are to the written word: an easier, digital method for creating and editing documents, which were once drafted by hand. CAD systems are used extensively to map infrastructure (e.g., roads, utilities, property, telecommunication networks) as well as for architecture plans and renderings, mechanical designs, and drawings used in civil and industrial design. Although geographers use these systems largely for mapping geospatial information, CAD systems are remarkably versatile and are used for applications as diverse as designing microchips; shipbuilding; aircraft, aerospace, and satellite design; automobile and engine design and rendering; textile and fashion design; robotics; and computer-assisted manufacturing.

CAD systems, such as Illustrator or CorelDraw software for drawing, offer great flexibility in representing graphical and spatial entities; however, unlike most drawing packages, CAD systems are designed for drafting especially complex and highly precise maps and plans. CAD systems are also very closely related to vector-based geographic information systems (GIS) and often provide inputs or outputs for GIS analysis. Early CAD systems focused on ease of graphic design and editing and, in so doing, relied on Cartesian coordinate systems and lacked database interfaces for linking graphic and spatial features to nonspatial attributes—both features essential to GIS. Contemporary CAD systems can work with geographical coordinate systems and readily permit database linkages between spatial and nonspatial data, meaning that there is no longer a sharp divide between CAD and GIS. GIS systems usually offer a wider range of analytic, geospatial, and modeling options than do CAD systems, particularly in the domain of topological modeling, but even these types of GIS functionality can be built into CAD systems using add-on software, scripts, and macros. In the areas of terrain modeling, surface modeling and rendering, and three-dimensional modeling, mapping, and animation, GIS and CAD are moving ever closer together because their modeling, visualization, and computational models are closely interrelated.

CAD, vector-based GIS, and drawing software share many concepts that make it relatively easy for users to move back and forth among systems. Phenomena are represented graphically as points, lines, and areas/shapes. Features of particular types (e.g., roads, streams, or census boundaries) are organized into common layers or levels. All the systems offer tremendous flexibility in how the data are symbolized, for example, by hue, value, texture, size, orientation, and shape. Principles of effective cartographic and visual symbolization and display apply just as strongly to CAD systems as they do to GIS and drawing software.

CAD files are used widely to archive and exchange geospatial information. Commonly used file types that can be found on the Web are .dwg and .dxf (AutoCAD formats) and .dng (Microstation/Intergraph format), which cannot be readily imported into most GIS.

Other related terms are computer-assisted mapping (CAM), computer-aided design (CAD), [Page 319]automated mapping/facilities management (AM/FM), computer-assisted drafting and design (CADD), and computer-assisted cartography.