Exploring Data Visually - Data Points: Visualization That Means Something - page 175

FIGURE 4-34 Filled contour map
CARTOGRAMS
A challenge with mapping regions, the choropleth map in particular, is that
larger regions always get more visual attention regardless of the data. They take
up more space in the physical world and on the computer screen. Cartograms
are one way to remedy this. Location is somewhat preserved, but geographical
areas and boundaries are not.
For example, a diffusion-based cartogram preserves boundaries but stretches
them out so that the area of regions match the data. For example, Figure 4-35
shows the UFO sighting data as a cartogram. Notice the shrinking of Texas
and swelling of California.
Obviously, the upside of cartograms is that areas fill the appropriate amount
of space, but the trade-off is less geographic accuracy. When your data is for
larger regions, with a wide range of sizes, this trade-off is worth it, but when
regions are uniform in size, a choropleth map is most likely a better fit.