Artificial reality - The Visualization of Spatial Social Structure - page 85

here (Figure 3.19). Again the even spread across the country can be noted
(Figure 3.20). Intriguingly, though, the network is most sparse in population
space where it is most concentrated on the ordinary map - in London. It is
no wonder that congestion is greatest where there are least roads per head of
population.

3.7 Stretching spacetime

A linear cartogram operates like an area cartogram but instead of
varying areas with values it is the map distances which vary with
values. Its construction is analogous to the azimuthal equidistant
projection,

but rather than physical distance varying with map

distance - cost of effort of travel are used.

(Lai, 1983, p. 33)

The difficulty of constructing area cartograms is due to the fact that they are
two-dimensional entities (Figures 3.21 and 3.22). One-dimensional cartograms
are simplicity itself to produce.
Imagine a one-dimensional, temporal cartogram of the human population of
the world ever born, from when the species began until the present day. Such
a cartogram would consist of a single line, with dates marked along its length
(Box 3.4). The distance between any two dates would be in proportion to the
number of people born between those times. Thus, the time line would be very
compact at the beginning, having its years widely spread towards the end. More
importantly, it is unambiguously the only solution to the problem of including
all people who have ever lived.
The number of dimensions of a cartogram can vary, limited in type only
by the imagination. A halfway house can be envisaged of a one-and-a-half-
dimensional cartogram, where some information independent of time is depicted
vertically up from the time-line cartogram, for example the proportion of the
population living in the various continents. Such a cartogram would be just as
simple to construct and, while appearing two-dimensional, the information is
of one dimension (place) within another (time). The second graph in Box 3.4
shows this.
The term linear has already been reserved in the literature on cartograms
to mean something other than one-dimensional. The most well-known reason
to draw these cartograms has been to fit place names in and so simplify the
mapping of a city's underground train system. Another well-known option is to
make the distances between places proportional to the time or cost required to
travel between them. 19 This can only be achieved for the, say, shortest travel

19 'The plotting of places in terms of accessibility metrics like time and cost distances is partic-
ularly valuable when communicable diseases are being studied and may frequently provide a fresh
perspective on the disease patterns occurring' (Cliff and Haggett, 1988, p. 267).