158 sYMBOLizaTiOn
Quantitative line data
If the data are in ordered or ranked categories
that imply differences in size, line
width can be varied. Thus, freeways are larger than state highways which in turn are
larger than county roads. In this case, the different categories may also be shown in
different hues as well. Boundaries are usually hierarchical so the lines for national,
state, county, and minor civil divisions should reflect that hierarchy with variations
in width and/or lightness (Figure 8.15).
Often data are collected that show amounts along routes. These can be shown
with lines that vary in width, called
flow lines (Figure 8.16). Examples are number of
cars along a road, amounts of a product shipped between two points, and number of
immigrants moving between two locations. For such symbols, the width of the line is
drawn proportional to the amount represented. The line may follow the actual route,
such as number of cars, or the route may be schematic, as for shipping or immigra-
tion.
City
County
State
National
Stream
Intermittent
Stream
