Designing and Choosing symbols 149
only for large areas, and density isn’t a primary concern, it is better to choose a dif-
ferent
kind of symbol, such as a proportional figure or choropleth.
Proportional and
Range-graded Point symbols
Symbols of varying sizes can be used to symbolize totals at a point. The shape most
frequently used is a circle, but squares, triangles, and even pictorial shapes can be
VERMONT
CATTLE & CALVES
1 DOT = 5,000
VERMONT
CATTLE & CALVES
1 DOT = 500
VERMONT
CATTLE & CALVES
1 DOT = 1,000
VERMONT
CATTLE & CALVES
1 DOT = 1,000
A
B
C
D
fIgURe 8.3.
(A) The dot value is too large so the pattern can’t be seen; (B) the dot value is
too small, which also obscures the pattern; (C) the dot value here is good, but the dots are too
small
to be easily seen; (D) the dots here are so large that they overwhelm the map.
150 sYMBOLizaTiOn
used. The size of the figure represents the quantity.
Proportional figures are con-
structed so that the
area of the figure is proportional to the value:
A =
π
R
2
. Thus, a
circle representing 1,000 people will be one-half as large in area as one representing
2,000 people. It is important to recognize that it is the area of the circle, not the
radius, that is two times as big (Figure 8.5). In this example, the radius of the larger
VERMONT
CATTLE & CALVES
1 DOT = 1,000
fIgURe 8.4.
Dot density maps have dots placed randomly within the enumeration areas.
Radius of Y is 1/2 that of X.
Area of Y is 1/4 that of X.
Radius of Y is .7 that of X.
Area of Y is .5 that of X.
X
X
Y
Y
The area of Square Y is 1/4 that
of Square X.
The area of Square Y is 1/2 that
of Square X.
