Positions, Networks, Fields, and Transformations - A Primer of GIS: Fundamental Geographic and Cartographic Concepts - page 172

PRINCIPLES OF GI AND CARTOGRAPHY Positions, Networks, Fields, and Transformations

Chapter 9

Positions, Networks, Fields,
and Transformations

GI can be changed in many ways, whereas maps are usually very difficult to
change—for example, copying a small map showing major cities of North
America on a single sheet of office paper to a wall-size poster. Certainly, GI,
like maps, is a form of geographic representation based on measurements,
observations, and relationships (see Chapter 2). But unlike maps, GI has not
been altered through a cartographic representation. Further, and most
importantly, GI can be transformed in various ways. Conventions usually
guide these transformations in both overt and subtle ways (see Chapter 11).
We can distinguish between three GI representation types: positions,
networks, and fields. The key issues for geographic representation and carto-
graphic representation related to the different GI types and transformations
between the GI types are the focus of this chapter. Things and events can be
represented as all of these types. Each offers different possibilities for
recording measurements, observations, and relationships. As a position, a
thing or event is represented as a discrete record of location and properties.
Not only is the thing or event fixed in space with a recording of its position
in a coordinate system, its properties are also recorded based on observa-
tions and measurements made at or of that position. Things and events rep-
resented as networks are recorded using an ordered arrangement of con-
necting points, called nodes (usually), lines, and sometimes areas. The things
and events must be recorded in association with one of these geometrical
network elements. Fields are used for nondiscrete things and events, which
include anything that can be observed or sensed, but usually does not have
clearly identifiable limits—for example, ozone, CO 2 , or soil pH.
Each GI representation type is recorded using a database (see Chapter 6)
or computer-based storage. This storage provides various ways to organize
and index the GI on the computer, which are usually determined by the soft-

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