Volume visualization - The Visualization of Spatial Social Structure - page 275

The basic two-dimensional flow maps showed numerous overlapping arrows.
When the change between two years was sought, even depicting the single differ-
ences could require two separate images. Depiction of spacetime flows of people
would have to be constructed in three dimensions. Theoretically there would be
a plane to represent every year, which would contain the changing population
cartogram. Places would be linked by tubes, the width of which, say, was in pro-
portion to the number of migrants. To prevent the image becoming too tangled in
practice, a measure of significant change would have to be found, similar to that
used in the two-dimensional case. Otherwise almost ten thousand tubes would
have to connect every pair of time planes. At least the origin and destinations
of migration would be obvious, even if the paths between them were, to say the
least, a little confused (Box 9.3).
The structure just described has not been created here; maybe it would just
produce a perplexing mess. To understand such a structure, even after generalisa-
tion, requires the development of new techniques to look into three dimensions. A
maze of tubes crisscrossing in spacetime will not reveal its structure through the
illumination of its outside surfaces. Cross-sections through the connections would
be confusing, and it is also not possible to simplify such a complex organisation
to a plane and retain its essential form.

Box 9.3 Three-dimensional structure

A complex three-dimensional structure is
sure to appear extremely confusing when
forced to fit on flat paper. These two graph-
ics show an experiment to project the space-
time distribution of unemployment and the
use of tubes to show migration flows across
space and time.

Eventually being able to rotate these
images is not enough. We need to be
able to get inside them to explore
and discover what the structure to the patterns may be. With 1980s home
computer graphics, we could only paint pictures of the outside and were
unable to see within.