The wood and the trees - The Visualization of Spatial Social Structure - page 227

8.3 Bars and pyramids

The persistent decline in London's employment over the past twenty-
five years or so has occurred despite an industrial structure which has
been consistently biased towards activities in which there has been
expanding employment nationally.

(Buck et al., 1986, p. 66)

How can we begin to understand how the economy appeared to falter in
London and how that was then reversed? 5 If we were trying to show the mul-
tivariate information about a single place in isolation, we would probably not
draw circles; we would use charts (Figures 8.2, 8.3 and 8.4).
The simplest chart is made up of bars, one bar for each variable, and its
height drawn in proportion to the value of that variable. Thus we could show,
for instance, the numbers of people employed in eight types of industry simulta-
neously. As the bars are reflected horizontally and vertically it becomes possible
to show the proportions of male and female, full and part time. There are clearly
limits to the number of places that could be compared, as the number of aspects
we choose to include increases.
One problem with the bar chart is that the order in which variables are placed
along the bar greatly influences the visual impression given, and the order is
arbitrary. If the order of the industries, say, were made the same as their national
ranking, then charts where a gradual rise was broken would show areas where
the industrial mix was at odds with what would be naively expected.
The bar chart is taken to one more level of detail when population pyramids
are constructed. These are simply two charts placed back to back and standing
vertically, usually used to depict the detailed age/sex structure of an area. What
is most important about these symbols (as with all glyphs) is that they create a
recognisable shape. It is the outline of the pyramid that is important, and this is
often simple enough to compare places across space, particularly if differences
are exaggerated. Finally, the pyramid can be reflected again, horizontally, to show
four related distributions as a cross (Box 8.2), which has been done for some of
the illustrations shown here 6 (Figures 8.5 and 8.6).

5 Migration patterns also strongly influence the relationships: 'In the London boroughs the dom-
inance of net out-migration tends to produce different relationships between the components of
labour-force change. In boroughs with increasing or stable economically active populations (which
are all suburban boroughs), the pattern is generally that net out-migration offsets large increases in
female economic activity' (Congdon and Champion, 1989, p. 188).
6 The role of London is of crucial importance to the developing geography of industrial structure.
Some early 1980s writers were especially prescient: 'For what we must remember above all about
service activities are that they are growing; that although they are increasingly dispersed within
regions, their growth is increasingly concentrated in areas within about 100 miles of London but
excluding London itself; and that in this respect especially, and in the close relationship of their
distribution to functional areas, their behaviour is unlike that of manufacturing' (Marquand, 1983,
p. 134).