GI and Cartography Issues - A Primer of GIS: Fundamental Geographic and Cartographic Concepts - page 63

colors for traffic signals are used, people can quickly understand where traf-
fic is slowed down or stopped. This is a meaningful use of a graphic variable
to communicate a complex thing. (See Chapter 10 for more discussion about
symbols and semiotics.)
Geographic representation involves choices with direct impacts on sym-
bols and semiotics. Whether it be traffic jams, soil pH, water flow, dispersion
of airborne pollutants, or household income, how the data is geographically
represented plays a huge role in what symbols can be used and how the
meaning and significance of the meaning can be communicated.
Color and Symbolization
The use of color in cartographic representation involves several important
choices. Value, hue, and saturation are graphical characteristics of color (see
Plate 3), which are most significant for pragmatic purposes (see Chapter 10
for further discussion). Color value refers to the different degrees of darkness
or lightness of a color. High values are light and low values are dark. Color
value is usually applied to distinguish ordinal data values—for example, soil
pH or population density. Color hue is what people normally refer to as
“color,” which is the distinction between blue, brown, red, yellow, and so on.
This distinction is a result of the ref lectance of different light wavelengths by
a surface. The ability to distinguish hue is commonplace among people in all
cultures, but the significance of individual colors can vary widely. Color hue
can be used to show nominal differences—for example, different states, types
of vegetation, planning zones—but should be used very carefully for numeri-
cal values because it is difficult for people to associate a large number of
hues with changes in values. Color saturation is the purity or intensity of a
hue. Saturation is used in conjunction with value and hue to enhance reader
perception of relationships and order of map features.
Organizational Structure of GIS, Software, Hardware,
and Peripherals
Organizations, software, hardware, and peripherals have great inf luences on
the possible choices for geographic representation and cartographic repre-
sentation. Nowadays the various aspects of geographic representation, carto-
graphic representation, conventions, and choices come together in the orga-
nization of GIS. A GIS always has an organizational aspect: people obtain
data from other people or organizations, share the results of their analysis or
mapping with other people, and coordinate the work related to GIS with
other people or organizations. Additional key aspects of the organizational
aspects of GIS are covered later in Chapter 12.
Key components of GIS organization are software, hardware, and
peripherals. GIS software contains the programs, interfaces, and even proce-
dures for processing data and making graphics and maps. Hardware per-
forms the operations of the software and makes displays and printouts. The