GI and Cartography Issues - A Primer of GIS: Fundamental Geographic and Cartographic Concepts - page 59

tude values are converted to a two-dimensional orthogonal network of x , y
values. The advantage is that unprojected geographic information can
readily be transformed to other projections as needed. Smaller areas are usu-
ally projected because the projected representations better correspond to
conventional maps that people have used for many years. In areas with
legally established coordinate systems or with clear conventions, the choice
of projection can be easy. In other areas, a few choices may be preferable
depending on the orientation, size, and accepted practices for the area in
question.
Projections in Practice
You should look at the distortions of the Mercator projection and the
recently popularized Peters projection in Figure 3.9. The widespread use of
the Mercator projection to show things and events at a global scale (which,
you should note, Mercator never did) leads to very sizeable distortions, espe-
cially in areas near the poles, but also in the latitudes where most of Europe
and North America are located (see Figure 3.10). These distortions led Arno
Peters to promote his adaptation of older projections, the Peters's projec-
tion, which has been widely adopted even though it introduces other distor-
tions. While the Peters's projection does not solve all projection problems, it
has made people more aware of the distortions inherent in projections.
Geographic Information and Maps Are Abstractions
Finally, we should note that projection is one type of abstraction, which can
be misused and even lied with. Sometimes this is obvious, but careful editing
can gloss over rough spots. Geographic information and maps involve many
other abstractions, which is why one of Mark Monmonnier's topics on carto-
graphic principles, uses, and abuses carries the title “How to Lie with Maps.”
Based on what you now know about projections, the claim that maps lie is
easy enough to refute. All maps must have distortions; therefore, some
would argue, what is called a “lie” is only a “distortion.”
Additional Fundamental Choices
The principle choices in geographic and cartographic representation high-
light key issues for the geographic information or map framework that
abstracts the infinite complexity of the world. This process of abstraction is
commonly called “data modeling” in GIS practice and teaching. Data model-
ing merges geographic representation and cartographic representation.
However, when using existing geographic information, other organizations
have already decided many aspects of data modeling. By keeping geographic
representation and cartographic representation separate, you can develop a
better understanding of the complexities of data modeling.