Envisioning information - The Visualization of Spatial Social Structure - page 14

Box 1.2 Printing in colour

The device first used to print the colour illustra-
tions in this topic was a ColorView 5912 plotter
printer manufactured by CalComp in 1988. The
plotter could produce pixels of eight colours by
overlaying sheets of magenta, cyan and yellow
film with an A4 resolution of 2048 by 1600
pixels. A greater range of colour was possible
by using dithered patterns of the eight colours
actually available. On-screen text could be more
satisfactorily produced through the use of anti-
aliasing techniques built into the computer soft-
ware.

A driver was specifically written to convert red-green-blue output from
the screen to the magenta-cyan-yellow form suitable for printing.
Each colour print, originally A4 size, could have over three million indi-
vidual bits of information, and took half an hour to print.

Different colours are perceived variably and convey loaded meanings on their
own, even more so in combination. The human eye is poor at focusing on blue.
Red and green do not combine to form reddish-green. Colour adds another level,
but not dimension, of complexity. The careful use of colour can convey more
of the depth of spatial organisation. In particular, when used in bivariate and
trivariate mapping, colour can show how several variables are related to each
other on a single map, although the keys are complex (Figure 1.8).
Trivariate mapping is both a contentious and potentially highly effective
technique. 11

It has been suggested that the printer's primary triplet of

cyan, yellow and magenta be employed 12 (or the computer's red, blue and

11 'It is far more difficult to distinguish the amounts of the three primary colors painted simul-
taneously onto a point in space, but it is possible (barely possible) to do so. Therefore a crude, but
effective, way exists for displaying three functions of three independent variables' (Staudhammer,
1975, p. 183).
12 '

maps with the same scale can be superimposed three by three. It is sufficient to transcribe
them on three different color films: cyan-blue, yellow, magenta-red' (Bertin, 1981, p. 163).

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