Projections - A Primer of GIS: Fundamental Geographic and Cartographic Concepts - page 95

6. Why is most GI projected to a two-dimensional, Cartesian coordi-
nate system?
Several reasons need to be considered. Much GI comes from maps with
such coordinate systems. Most GI is used to make planar maps. Most GIS
are designed to store two-dimensional coordinate locations.
7. Why should you never combine GI from different projections?
GI from different projections for the same area will be in different coordi-
nate systems that do not align properly.
8. How can positional distortion be measured?
For small-scale maps, Tissot's indicatrix provides a good graphical indica-
tor. Large-scale maps, showing small areas, require the use of statistical
measures.
9. What is the difference between a geoid and a spheroid?
A geoid is a more accurate representation of the earth's surface, accounting
for local variations. A spheroid is a perfectly round form that fails to
account for local variations and the oblateness of the earth resulting from
its spin.
10. Why are Mercator and Peters projections technically satisfactory?
Why do people consider the Mercator projection to be a bad projec-
tion?
The Mercator projection is well suited for compass navigation at sea. The
Peters projection is a compromise that offers a different way of represent-
ing the world. The overuse and ill-suited use of the Mercator projection to
show regions of the world has led to the Mercator acquiring a bad reputa-
tion.
Chapter Readings
Jones, C. (1997). Geographical Information Systems and Computer Cartography . Upper
Saddle River, NJ: Prentice Hall.
For a fascinating, if wide-reaching, biography and study of a person who was instru-
mental in determining the elliptical shape of the earth, see:
Terrall, M. (2002). The Man Who Flattened the Earth: Maupertuis and the Sciences in the
Enlightenment . Chicago: University of Chicago Press.
For information about the basic mathematical principles of cartography, see:
Cotter, C. H. (1966). The Astronomical and Mathematical Foundations of Geography . New
York: Elsevier.
For a history of projections, see:
Montgomery, S. (1996). Naming the Heavens: A Brief History of Earthly Projections.
Science as Culture , 5 (25), 546-587.
For a very thorough history of projections, see:
Snyder, J. P. (1993). Flattening the Earth: Two Thousand Years of Map Projections . Chi-
cago: University of Chicago Press.