Cartograms and Diagrams 193
Some authors consider the noncontiguous type to be the most crude form of the
cartogram and criticize the sacrifice of continuity. However, it is easy to create even
with illustration software.
VaRiaTiOns
There are a number of variations of value-by-area cartograms. The rectangular car-
togram, popularized by Raisz, uses a variety of rectangles to approximate the shapes
of countries or states. This type is popular in atlases.
Dorling cartograms, which
were invented by Daniel Dorling, replace the enumeration areas by uniform abstract
shapes, normally circles (Figure 10.4); there is no attempt to maintain shape or topol-
ogy. It is best if the shapes do not overlap so that each
enumeration area can be
identified, but in doing so, the figures are moved from their actual geographic loca-
tions. The method for determining the circles or squares is the same as that used for
proportional circles and squares. The
Demers cartogram is a variation of the Dorling
cartogram, but uses squares to represent enumeration areas and permits greater con-
tiguity than circles (Figure 10.5).
Bivariate Cartograms
Any type of value-by-area cartogram can represent multiple variables.
Bivariate car-
tograms, like bivariate choropleth maps, show two variables, such as population and
income. One variable is shown as the cartogram, while the second variable is shown
by color or shading, as with choropleth maps Figure 10.6 is a simple, noncontiguous
cartogram in which the population of each state forms the cartogram, and violent
crime is shown with shades of gray.
Finally, contiguous cartograms likewise portray the enumeration area as the car-
Vermont Population
by County
