Designing and Choosing symbols 155
the number of blocks since some are necessarily hidden. Little has been done in test-
ing reader perceptions of these symbols.
design considerations
Placement
of Circles
If circles represent point phenomena, they are ideally located at the point. For circles
that represent aggregates over regions, the options are to place the circle in the center
of the region or over the most dense area. In most cases it is best to center the circles
within the enumeration areas. Ideally, the circle fits entirely within the enumeration
area and doesn’t overlap boundaries; this is a major factor in determining the radius
of the circle. However, because large quantities are often found in small areas, this
is not always possible. In such cases, it may be necessary to place a circle outside the
enumeration
area with a callout, as in Figure 8.11.
Filling Circles
Often, proportional symbols are filled with a hue or pattern to make them more leg-
ible because an open circle lacks contrast. Unless the circle represents two variables
it is not good practice to use lightness as well as hue, such as shades of gray or red,
in an effort to enhance the quantities represented. This
is called redundancy and
although there is some debate over the practice, there has been no testing with map
users. Redundancy can be confusing to the reader who assumes that the lightness
steps represent a second variable (Figure 8.12).
Overlapping Circles
Frequently, circles overlap, as in Figure 8.13, where a number of cities are quite close
to one another. If the circles aren’t filled with a hue or pattern, they appear as a tan-
Lake
