Mapping the Globe with Latitude and Longitude
How do you give a friend directions to your home? You might use street names
and tell her where to turn right or left. Or you might use directional terms to say
you are north, or southeast, for example, of a landmark. But how would you tell a
satellite where your home is? Most satellites locate points on the surface of the
Earth using latitude and longitude. These two terms represent a coordinate system
that covers the entire globe. Satellites and navigation systems can use this system
to locate anything on Earth.
So, to give a satellite your address, you would tell it where you are on the Earth’s
latitude and longitude grid. For example, Galveston, Texas, is located at about
latitude 29 degrees north and longitude 94 degrees west. For greater precision,
each degree of latitude and longitude is divided into 60 minutes. A more exact
address for Galveston is: 29n18, 94w48, or latitude 29 degrees 18 minutes north,
longitude 94 degrees 48 minutes west.
You can look up latitude
and longitude coordinates
for cities on a map or
globe or on the Internet.
Try finding General
Motors headquarters – it’s
at 42 degrees north and 20
minutes, 83 degrees west
and 3 minutes; or 42n20,
83w03 for short.
Geography Glossary
latitude lines
Imaginary lines running horizontally around the globe. Also called parallels,
latitude lines are equidistant from each other. Each degree of latitude is about 69
miles (110 km) apart. Zero degrees (0°) latitude is the equator, the widest
circumference of the globe. Latitude is measured from 0° to 90° north and 0° to
90° south—90° north is the North Pole and 90° south is the South Pole.
longitude lines
Imaginary lines, also called meridians, running vertically around the globe.
Unlike latitude lines, longitude lines are not parallel. Meridians meet at the poles
and are widest apart at the equator. Zero degrees longitude (0°) is called the prime
meridian. The degrees of longitude run 180° east and 180° west from the prime
meridian.
geographic coordinates
Latitude and longitude lines form an imaginary grid over the Earth's surface. By
combining longitude and latitude measurements, any location on earth can be
determined. The units of measurement for geographic coordinates are degrees (°),
minutes ('), and seconds ("). Like a circle, the Earth has 360 degrees. Each degree
is divided into 60 minutes, which in turn is divided into 60 seconds. Latitude and
longitude coordinates also include cardinal directions: north or south of the
equator for latitude, and east or west of the prime meridian for longitude. The
geographic coordinates of New York City, for example, are 40° N, 74° W,
meaning that it is located 40 degrees north latitude and 74 degrees west longitude.
Using minutes and seconds as well as degrees, the coordinates for New York
would be 40°42'51" N, 74°0'23" W. (Latitude is always listed first.) A less
common format for listing coordinates is in decimal degrees. The Tropic of
Cancer, for example, can be expressed in degrees and minutes (23°30' N) or in
decimal degrees (23.5° N).
hemisphere
A hemisphere is half the Earth's surface. The four hemispheres are the Northern
and Southern hemispheres, divided by the equator (0° latitude), and the Eastern
and Western hemispheres, divided by the prime meridian (0° longitude) and the
International Date Line (180°).
equator
Zero degrees latitude. The Sun is directly overhead the equator at noon on the
two equinoxes (March and Sept. 20 or 21). The equator divides the globe into the
Northern and Southern hemispheres. The equator appears halfway between the
North and South poles, at the widest circumference of the globe. It is 24,901.55
miles (40,075.16 km) long.
prime meridian
Zero degrees longitude (0°). The prime meridian runs through the Royal
Greenwich Observatory in Greenwich, England (the location was established in
1884 by international agreement). The prime meridian divides the globe into the
Western and Eastern hemispheres. The Earth's time zones are measured from the
prime meridian. The time at 0° is called Universal Time (UT) or Greenwich Mean
Time (GMT). With the Greenwich meridian as the starting point, each 15° east
and west marks a new time zone. The 24 time zones extend east and west around
the globe for 180° to the International Date Line. When it is noon along the prime
meridian, it is midnight along the International Date Line.
International Date Line
Located at 180° longitude (180° E and 180° W are the same meridian). Regions
to the east of the International Date Line are counted as being one calendar day
earlier than the regions to the west. Although the International Date Line generally
follows the 180° meridian (most of which lies in the Pacific Ocean), it does
diverge in places. Since 180° runs through several countries, it would divide those
countries not simply into two different time zones, but into two different calendar
days. To avoid such unnecessary confusion, the date line dips and bends around
countries to permit them to share the same time.
Tropic of Cancer
A line of latitude located at 23°30' north of the equator. The Sun is directly
overhead the Tropic of Cancer on the summer solstice in the Northern Hemisphere
(June 20 or 21). It marks the northernmost point of the tropics, which falls
between the Tropic of Cancer and the Tropic of Capricorn.
Tropic of Capricorn
A line of latitude located at 23°30' south. The Sun is directly overhead the
Tropic of Capricorn on the summer solstice in the Southern Hemisphere (Dec. 20
or 21). It marks the southernmost point of the tropics.
Arctic Circle
A line of latitude located at 66°30' north, delineating the Northern Frigid Zone
of the Earth.
Antarctic Circle
A line of latitude located at 66°30' south, delineating the Southern Frigid Zone
of the Earth.
globe
The most accurate map of the Earth, duplicating its spherical shape and relative
size.
map projections
Two-dimensional representations of the three-dimensional Earth. Because
projections attempt to present the spherical Earth on a flat plane, they inevitably
produce distortions. Map projections are numerous and complex (e.g., there are a
variety of cylindrical, conic, or azimuthal projections). Each projection has
advantages and serves different purposes, and each produces different types of
distortions in direction, distance, shape, and relative size of areas. One of the most
famous projections is the Mercator, created by Geradus Mercator in 1569. It is a
rectangular-shaped map in which all longitude and latitude lines are parallel and
intersect at right angles (on a globe, meridians are not parallel, but grow narrower,
eventually converging at the poles). Near the equator, the scale of the Mercator is
accurate, but the farther one moves toward the poles, the greater the distortion—
Antarctica in the far south and Greenland in the far north, for example, appear
gigantic. The Mercator projection was used well into the 20th century, but has
now been superseded by others, including the widely used Robinson projection.
The Robinson projection is an elliptical-shaped map with a flat top and bottom.
Developed in 1963 by Arthur H. Robinson, it is an orthophanic (“right appearing”)
projection, which attempts to reflect the spherical appearance of the Earth. The
meridians, for example, are curved arcs, which gives the flat map a threedimensional appearance. But to convey the likeness of a curved, three-dimensional
globe, the Robinson projection must in fact distort shape, area, scale, and distance.
The Albers, Lambert, Mollweide, and Winkel Tripel are some of the other
commonly used map projections.