Geography Reference
In-Depth Information
relative importance of the political units they mark. In Figure 5-4, the line that separates the
United States and Canada is thicker than the lines that separate the states and provinces. Sim-
ilarly, lines that symbolize roads often vary in thickness in proportion to the width of the high-
way or number of lanes.
Flow lines
indicate movement, travel or trade along a given route or between two points.
On some maps, the thickness of the lines varies in direct proportion to the quantity or volume
of the flow. Thus, on a map of immigration, arrows of varying widths may be used to indicate
the volume of movement between sender and receiver regions (as shown in Figure 5-5).
Isolines
connect points of equal value with respect to a certain phenomenon. The contour
lines shown in Figure 5-3b are an example. Similarly, daily weather maps often contain
isolines that connect points with identical atmospheric pressure or the day's projected high
temperature.
Figure 5-5:
This
map uses flow
lines of different
widths to indicate
volume of immig-
ration.
Area symbols
Area symbols use gray tones or colors to depict phenomena that characterize areas as opposed to
points or lines and are separated into two basic varieties.
Nominal symbols
identify qualitative characteristics or phenomena that pertain to areas or
regions. Figure 5-6, for example, uses nominal symbols to identify official languages of South
