The wood and the trees - The Visualization of Spatial Social Structure - page 224

8.2 Circles, pies and rings

This type of presentation makes it easy to grasp the interacting rela-
tionships between age and race. For example, there are tracts in which
most of the children are nonwhite but a majority of the elderly are
white.

(Applied Urbanetics INC, 1971, p. 4)

The basic shape used up to now in this topic to represent spatial objects,
when they were large enough to have shape, has usually been the simplest - the
circle. This choice was made to avoid the shape distracting attention from the
overall impression of the image. Rotation has no effect on the circle, but it can
reflect one variable through its size.
Size is used here to represent the total population of a place. Circles, when
divided into two rings, can be used to show discrete states at two points in time
across many places. Could the circle be subdivided further to show the relative
sizes of different sections of that population and then coloured by variables such
as majority ethnicity at each age?
Pie charts may well be the first possibility to spring to mind. These appear
ideal; a dozen subgroups could be shown simultaneously. The circle could, for
instance, be cut into male and female slices, these could then each be divided
into the proportions working and not working, further subdivided into full-time
and part-time workers and so on. There are, however, many problems associated
with this.
We are not particularly good at comparing angles, especially when they are
presented to us at differing orientations, or at gauging the slight differences in
the area of the slices. Worse still, when we are presented with more than a couple
of these symbols, we quickly become visually perplexed. We see a multitude of
individually complicated parts, which we cannot easily comprehend as a whole.
The basic requirements of a glyph is that not only should it form an acceptable
single entity individually but that, when viewed together, a group of glyphs
should melt into a gestalt collection so that overall patterns in the multivariate
information can be discerned. A group of leaves can combine into differently
shaped trees and groups of trees create different looking woods. We must be
able to see the woods, not just the trees, from pictures which, without added
imagination, simply show the branches and the leaves. 3
The need for glyphs to work in aggregate as well as alone explains why
many initially promising ideas often fail in practice. One method envisaged for

3 Individually well-designed glyphs may fail to combine into a single overall image: 'The dimen-
sions of the trees and castles also lack perceptual integrity.

...

They do not provide their observer a
single image or concept or gestalt that he or she can process and remember, binding together the
values of all the coordinates of the point. For example, polygons and faces tend to provide observers
with such a concept, while glyphs and bar charts tend to look simply like the accretion of their
several elements. Trees and castles appear to fall in the latter category' (R.J.K. Jacob, in Kleiner
and Hartigan, 1981, p. 271).