||The use of digital computers, mapping software and computer-driven display units to design or produce maps as well as to develop databases employed in map production. Computer-assisted cartography (also called digital cartography) is somewhat older than geographical information systems, a technological specialty concerned more with the storage, retrieval and analysis of spatial data than with cartographic display per se. Because computers are used widely in all phases of cartographic design and production, the adjective computer-assisted has become somewhat redundant insofar as almost all contemporary map production is at least partly computer-assisted.
Map projections, which often require repeated evaluation of complex mathematical formulae, were among the earliest cartographic applications of the computer (Snyder, 1985). Calculation of projected coordinates preceded by several years the automatic plotting of grid lines, boundaries and other geographical features. In the 1950s geographers and planners discovered that a computer could generate a crude map on an electric typewriter or line printer designed to print alphanumeric characters aligned in six or eight rows per inch down the page and in ten columns per inch across (Tobler, 1959). Despite this coarse resolution, the widely available high-speed line printer promoted inexpensive experimentation with choropleth maps as well as the convenient display of trend surfaces and other computationally demanding isoline maps.
Display quality improved markedly in the late 1960s and early 1970s with the introduction of plotters able to raise or lower a ballpoint or liquid-ink pen and draft curved lines by moving it simultaneously in the X and Y directions. Adept at drawing lines and labels, pen-plotters could also produce crude line-pattern area symbols for choropleth and land-use maps (Monmonier, 1982). Although the digital plotter never rivaled the ink pen or engraving tool in the hand of a skilled drafter, development of high-resolution large-format film plotters in the late 1970s provided efficient machine-controlled generation of photographic negatives used in colour printing. Government agencies and large commercial mapping firms that could afford the massive investment began to abandon drafting pens in favour of the digitizers and electronic scanners required for the \'capture\' or \'conversion\' (see digitizing) of digital cartographic data. Despite high initial costs, cartographic databases promised less expensive production of updated editions as well as increased cost recovery through secondary uses (Morrison, 1980).
Further advances in display technology in the 1980s encouraged university cartographic laboratories and other small map producers to abandon manual, non-electronic drafting. Improved cathode ray tubes and highly interactive illustration software allowed rapid placement of symbols and labels as well as efficient map editing. Toner replaced ink with the advent of high-resolution laser printers able to integrate precise, aesthetically pleasing type with crisp linework and carefully controlled graytones. Page-layout software and ultra-high-resolution imagesetters revolutionized publication design and pre-press production in the 1990s, when publishers began to require electronic versions of authors\' text and graphics. Further change is inevitable as a consequence of colour monitors, inexpensive colour printers and the World Wide Web, which supports broad dissemination without the expense and delay of printing.
Digital computing and electronic display challenged cartographers to automate two basic operations: label placement and line generalization. Label placement proved more straightforward: priority rankings describing preferred locations for feature-and placenames allowed algorithms to not only avoid overlapping labels but also provide aesthetically acceptable solutions that maximized the number of labeled features ( Jones, 1997, pp. 259-62). By contrast, line generalization proved an enigmatic problem with many facets and richly varied solutions. Although computerized strategies allow mapmakers to smooth and simplify line symbols, eliminate inconsequential point and area features, purge extraneous points from the list of coordinates, consolidate nearby polygons and exaggerate details for clarity, manual intervention is almost always necessary when a substantial reduction in scale demands lateral displacement of close, similarly aligned features (McMaster and Shea, 1992).
Other noteworthy developments include specialized data structures for the efficient storage and ready retrieval of spatial data (Laurini and Thompson, 1992); geocoding schemes for representing the topological structure of the urban street grid and census enumeration units (Trainor, 1990); more efficient methods for displaying and analysing terrain (Raper, 1989) and tools for automated line-following, edge-matching and other aspects of developing and maintaining a geographical database. Also important are graphical interfaces that promote the integration of mapping with a variety of computational processes, including automated recognition of disease clusters (Openshaw et al., 1987), simulation of toxic plumes in groundwater or atmosphere, and identification of shortest-path highway routes. Optimal routing is a particularly useful addition to automated highway navigation systems that continually update a detailed local street map showing the vehicle\'s current location. By introducing time and motion as visual variables, interactive computer graphics and animated mapping have vastly enhanced cartographic reconstructions and simulations of complex events and processes.Â (MM)
References Jones, C.B. 1997: Geographical information systems and computer cartography. London: Longman.Â Laurini, R. and Thompson, D. 1992: Fundamentals of spatial information systems. London: Academic Press.Â McMaster, R.B. and Shea, K.S. 1992: Generalization in digital cartography. Washington, D.C.: Association of American Geographers.Â Monmonier, M. 1982: Computer-assisted cartography: principles and prospects. Englewood Cliffs, NJ: Prentice-Hall.Â Morrison, J.L. 1980: Computer technology and cartographic change. In D.R.F. Taylor, ed., The computer in contemporary cartography. New York: John Wiley and Sons, 5-23.Â Openshaw, S. et al. 1987: A Mark 1 Geographical Analysis Machine for the automated analysis of point data sets. International Journal of Geographical Information Systems 1: 335-58.Â Raper, J., ed., 1989: Three-dimensional applications in geographical information systems. London: Taylor and Francis.Â Snyder, J.P. 1985: Computer-assisted map projection research, Bulletin 1629. Reston, Virginia: US Geological Survey.Â Tobler, W.R. 1959: Automation and cartography. Geographical Review 49: 526-34.Â Trainor, T.F. 1990: Fully automated cartography: a major transition at the Census Bureau. Cartography and Geographic Information Systems 17: 27-38.
Suggested Reading Masser, I. and Blakemore, M., eds, 1991: Handling geographical information: methodology and potential applications. Harlow, Essex: Longman.Â Monmonier, M. 1985: Technological transition in cartography. Madison, WI: University of Wisconsin Press.