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Tyner indb
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Bog'liq Judith A. Tyner. Principles of map design. New York. „The Guilford Press”, 2010why Use cartograms?
Cartograms of any type have a strong visual impact. Because they represent an
unusual view of the world or an area, they attract reader attention. This is an impor-
tant reason for choosing a cartogram instead of a conventional map. Often we are
concerned with magnitudes and want to make a stronger impression of relative val-
ues than could be made with a conventional choroplethic or isarithmic map. On a
conventional population density choropleth map by state, some small states with
high population density are barely noticeable, even when shaded black or red, but
on a population value-by-area cartogram of the United States, some large geographic
areas in the western states appear very small because of the low population densities
and New Jersey becomes very large (Figure 10.3). Conventional maps must show
sizes with complex symbols; therefore a graduated-circle map, for example, does not
have the same impact as a cartogram.
Both kinds of value-by-area cartograms, contiguous and noncontiguous, share
some characteristics or features that make them useful cartographic devices. They
have a strong visual impact; they permit the representation of distributions that might
be obscured by variation in enumeration sizes if mapped by conventional means; and
because there is little unnecessary detail, they may offer clearer representations of
some distributions.
There is no generalization of data on cartograms. There is no loss of detail
through generalization into categories as there is with choroplethic maps. Although
some readers and even cartographers are disturbed by the apparent lack of accu-
racy, cartograms are a legitimate and useful means of displaying geographic data. Of
course, because of their strong visual impact, cartograms are useful when the intent
of the map is to persuade.
fIgURe 10.9.
Variation on an isochronic (equal time) map. The lines represent driving time
and the locations are in their correct geographic positions.
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