Exploring Data Visually - Data Points: Visualization That Means Something - page 511

FIGURE 4-29 Connections between locations

REGIONS

To maintain the privacy of individuals and to keep personal addresses hidden,
it's common to aggregate spatial data before releasing it. Sometimes it's not
possible to make estimates at a higher granularity because it would be too
big of an undertaking. For example, it's rare to see global data more than
country-specific because it's difficult to get a big enough sample in every
country for such high detail.

FIGURE 4-30 (following page)
Categorizing data for more
specific views