Introduction
An Interest in Map Projections
A cartographic projection is a transformation
(also called mapping) from a
round surface to a plane. There are many different
projections, since
there are several interesting or useful properties to
fulfill. For instance, it would be desirable to
keep shape, distance and area relationships exactly as
in the original surface. Unfortunately, it can proved that there is
not and there will never be such a perfect projection: every one is
bound to distort at least part of the mapped region.
So cartography is an art and science of trade-offs and guidelines
for designing and choosing the least inappropriate projection for
each purpose.
I have always liked playing with world maps and wondered how
computers could be used for mapping. I spent a good time
deducing formulas
for projecting radius, latitude and longitude
into cartesian x and y. Of course, I could only
draw coordinate grids until the day I got a public-domain
database of geographical coordinates (at first my PC-XT
spent over one hour to draw a rough map).
My Own Projection
After some time I started devising my "own" projections (actually
I had little access to map bibliography, so I could have
reinvented the wheel). This projection of mine was
inspired by both Sanson's,
Flamsteed's and Eckert's works. It closely resembles
Eckert's V and VI, and also some of Wagner's
projections.
|
| My pseudo-Eckert map
|
This projection's mathematical derivation is presented in
Uma Projeção Cartográfica
Equivalente, Portuguese gzipped
PostScript 92KB
The simple application I wrote to draw maps is somewhat
restricted but effective. (luckily nowadays it
takes seconds, not hours).
What Can Be Learned Here
The next pages present basic projection concepts, which
properties are important for each map application, why there is
a diversity of maps, how projections are designed, how maps can be
misleading and how to choose a good projection for world maps.
More
than a catalog of projections, I have attempted to present
cartographical concepts in context; unavoidably, several
important projections are discussed in more than one place
(e.g., while explaining its mathematical foundations and when
listing projections with similar features).
 |  |  |  |  | | www.progonos.com/furuti February 13, 2007 |
