Name the two coordinate systems used by the
On most charts, 60 nautical miles equals how
many degrees of latitude?
Convert 23.54N and 120.38W to tenths of a
When you use the Universal Transverse
Mercator (UTM) grid, how is a grid zone
Grid zone 27R is between what latitude and
What is normally the smallest grid zone used
with the UTM grid system?
The Universal Polar Stereographic (UPS) grid
system is used in what region of the globe?
AREAS OF THE GLOBE
In meteorology and oceanography, several terms
are used to describe sections of the world. Northern
Hemisphere refers to the half of earth north of the
equator; Southern Hemisphere refers to the area south
of the equator. Similarly, Western Hemisphere refers to
the half of earth from the prime meridian westward to
the international date line; Eastern Hemisphere refers to
the half from the prime meridian eastward to the
international date line. You will see frequent references
to the tropical region, or the Tropics. The Tropics is the
belt surrounding earth that lies between the tropic of
Cancer at 23½°N and the tropic of Capricorn at 23½°S.
In meteorology, however, this region may generally be
considered the belt between 30°N and 30°S.
Geographically, the area of earth north of the Arctic
Circle at 66½°N and south of the Antarctic Circle at
66½°S are the polar regions. Between the Tropics and
each polar region lies the area referred to as the middle
Figure 4-8.Rhumb line and great circle tracks on a great
circle chart (gnomonic projection).
latitudes (or the mid-latitudes). Based on annual
temperature changes, the Tropics, mid-latitudes, and
polar regions are also respectively called the Torrid
Zone, the Temperate Zones, and the Frigid Zones.
These terms are generally falling into disuse.
Several types of modifications to the shape of earth
are made to allow the earths surface to be represented
on flat paper charts and displays. These modifications
are called "projections." The most common projections
used in meteorology and oceanography are the
Mercator projections, Polar Stereographic projections,
and the Lambert-Conformal Conic projections, as
shown in figure 4-7. Figure 4-7 also indicates the
properties of these projections and their intended uses.
You will often see references to great circle routes
or tracks. A great circle track represents the shortest
distance between two points on the surface of earth or
on a globe, such as if a string were to be stretched
between the two points. Great circle routes are planned
on a special chart projection called a gnomonic
projection. These projections are similar to polar
projections, except the plain of the chart is tangent to the
earth at the center of the area charted. Figure 4-8 shows
a gnomonic projection with a great circle route and a
rhumb line track between two ports. The rhumb line
track is a straight line drawn between two points on a
Mercator projection, and may also be called a "Mercator
track." Notice that the great circle route is about 800
nautical miles shorter than the rhumb line track due to
the curvature of the earth. Figure 4-9 shows the
identical routes drawn on a Mercator projection.
The scale of a chart refers to a comparison of the
distances shown on a chart to the actual distance on the
surface of earth. A scale may be a comparative ratio
Figure 4-9.Rhumb line and great circle course on a