108 THe geOgRaPHiC anD CaRTOgRaPHiC FRaMeWORK
the equator, a graphic scale for each parallel can be constructed. Figure 6.17 illus-
trates such a scale for a cylindrical (Mercator) projection with an equatorial scale of
1:1,000,000.
There are many cylindrical projections. Although they all have a family resem-
blance, they may be constructed to preserve different properties. For example, there
are cylindrical equal-area, cylindrical conformal (Mercator), and several compromise
cylindrical projections. These projections vary only in the spacing of the parallels.
A subgroup of the cylindricals that is sometimes described are the
pseudocy-
lindrical projections. These projections have straight parallels with the meridians
equally spaced, but the meridians are curved.
Probably the best known projection is the Mercator projection (Figure 6.18),
which is a cylindrical conformal projection. It is also one of the most misused of
the projections. Gerardus Mercator (Gerard Kramer) created the projection in 1569
to solve a particular mapping problem. The 16th century was a time of exploration
and yet a period when few navigational aids were available to sailors. The compass
existed and the tools to determine latitude, but longitude was difficult to determine
at sea, and great circle routes were hard to follow. The navigator needed a chart that
would allow him to make a landfall, despite his relatively poor instruments. Although
a short route was desirable, finding port was more important. Mercator’s projection
was designed to show constant compass directions (rhumb lines) as straight lines,
which means that a simple protractor could be used to read and plot compass angles
(ship’s course) correctly (Figure 6.19). Because it was conformal, the shapes of small
features, such as bays and harbors, were correctly represented. This was a major
breakthrough for navigation at the period.
Unfortunately, the Mercator projection has been much abused. Because of its
rectangular shape and the neat appearance of the graticule, because it is easy to draw
and fits nicely on a page, it has been widely used for maps of the world, especially for
wall maps in schools. Many significant misconceptions were produced in the minds
of generations of students because of this projection’s severe distortion of area. Com-
monly, students would wonder why Greenland was an island, but South America
was a continent. Because areal distortion is especially great in the high latitudes,
Greenland appears to be about the same size as South America, whereas it is actually
about the size of Mexico. In addition, since many people assume that a straight line
between two points is the shortest distance on any map, erroneous ideas of distance
result. Figure 6.20 shows the relationship between a rhumb line and a great circle
Equator
miles
Equator
0
100
200
300
400
500
600
50°
50°
30°
10°
30°
10°
