Choices in How We Make Representations - A Primer of GIS: Fundamental Geographic and Cartographic Concepts - page 43

common example occurs between the coordinate system and the projection.
In many cases, the cartographic projection is the same as the projection used
for the coordinate system. In these cases, it's clear how the relationship
between the geographic and the cartographic representations makes it easier
for cartographic communication. Staying with one projection means no
transformation between projections is required, which limits the potential
for distortions to be introduced. We need to consider how when the geo-
graphic representation and the cartographic representation use different
projections, the potential distortions to areas, angles, shapes, distances, and
directions can lead to many small errors or quite large errors. Combining
the geographic information for monitoring river flooding in northern Illi-
nois will be much more difficult if different projects and coordinate systems
are used.
In summary, geographic representation and cartographic representa-
tion should always be considered together when examining or developing
geographic information or maps for cartographic communication. Although
the media for geographic information and maps are vastly different and the
types of communication vary greatly, the parallels are great enough that with
some exceptions the basic issues for cartographic communication apply to
both.
Cartographic communication, in the most general sense, relies on dis-
tortions. As Mark Monmonier (1991) writes:

A good map tells a multitude of little white lies; it suppresses truth to help
the user see what needs to be seen. But the value of a map depends on how
well its generalized geometry and generalized content reflect a chosen
aspect of reality. (p. 25)

Although some cartographers find this view dismissive of cartogra-
phers' labor, it highlights how distortions are necessary for cartographic
communication to succeed. Perhaps we should add the important note that
this also means that we need to be especially on guard when working with
material prepared under a cartographic license that is ambiguous.
For cartographic communication, we should pay special attention to the
following characteristics of maps:

Scale What is the relationship between units on the map

and the same units on the ground? What simplifica-
tions accompany the scale?

Projection What kind of distortion does the projection intro-

duce to areas, angles, shapes, distances, and direc-
tions?

Symbolization How do symbols exaggerate or minimize features on

the map? How does the cartographic communication
benefit from the chosen symbols? What is the best
measurement framework? Nominal, ordinal, interval,
ratio?