GI and Cartography Issues - A Primer of GIS: Fundamental Geographic and Cartographic Concepts - page 62

focusing the representation on specifics, but runs the risk of losing critical
details necessary for using the geographic information and maps. Coming
back to the traffic jam example, a detailed breakdown of the traffic jam
length and average speeds in individual lanes may be useful for showing rela-
tionships between entering traffic and the traffic jam, but could add too
much detail for a communication goal of showing simply where the traffic
jam is and how long it lasted.
Scale
The scale , or the relationship between a unit of distance on the screen or
map to the same unit of distance on the ground, represents a critical choice.
If the scale is large (showing a small area), a great amount of detail can be
represented. If the scale is small (showing a large area), then less detail can
be shown. (Chapter 5 presents more on scale.) This relationship of scale to
detail and area constrains maps greatly and has impacts on geographic infor-
mation. Although computers allow for zooming in at different scales to data,
data captured at a small scale becomes very inaccurate when it is zoomed in
to. What scale is chosen, whether for geographic information or maps,
impacts both the geographic representation and the cartographic represen-
tation. (See Plate 2 for graphic symbols used in cartographic representation.)
Symbolization
A fundamental choice for cartographic representation is the symbolization.
Semiotics , the study of signs, helps us to understand the meaning of symbols
and how symbols take on meaning, both individually and through relation-
ships with other symbols. Significant choices for cartographic representation
involve symbols.
At a fundamental level, the choice of cartographic symbols and
semiotics can be compared to a language. In the “cartographic language,” a
limited set of graphic variables is available for “writing” a map. Building on
Bertin's earlier work on general graphic variables, several cartographers
identified size, pattern, shape, color value, color hue, color saturation, tex-
ture, orientation, arrangement, and focus. The graphic variables can be com-
bined in myriad ways, but it is clear that some variables are more associated
with difference in quantities—for example, size—than others. Effective carto-
graphic communication depends on how well the map creator matches
graphic variables to the spatial dimensions of the things, events, and associa-
tions.
Through semiotics, both the cartographic creator and the reader can
assess the connection between the symbols and the represented geographic
things and events. The Minnesota Department of Transportation depicts
traffic volumes in the Twin Cities using the three colors green, yellow, and
red. The system is extremely effective in rapidly communicating traffic slow-
downs. In spite of the complicated highway network, because conventional