The wood and the trees - The Visualization of Spatial Social Structure - page 247

It is a mistake to think that these symbols can add another dimension to the
two we have on paper. 17 Glyphs show multivariate structure, not multidimen-
sional form. We can look at a lot of categorical aspects of many places in space
simultaneously. We cannot see how some feature varies with, say, place and
varying wealth, multiparty voting or disease in spacetime.
Varying the features of an object is not a good substitute for varying its
position. Features of an object have no geometry and thus a limited ability to show
only a few values. To get a real extra dimension, beyond the first two, we must
begin to think in terms of volume and the next, penultimate chapter, of this topic.
17 However, the more effective the technique, the greater is the information that can be shown:
' ... the ability of humans to analyze effectively spatial distributions is alleged to deteriorate progres-
sively as the number of variables increases, inter-relationships among variables becomes subtle, and
the magnitude of variations decreases. This suggests that cartographic presentation must demand as
little mental computation and conceptualization as possible if the full potential of creative intuition
and decision making is to be realized. If the cartographer can develop more effective data reduction
techniques, and the map reader can be taught to understand their underlying concept (i.e., readily
decode them), then the amount of information communicated by a single map might be greatly
increased' (Muehrcke, 1972, pp. 19 - 25).