Chapter 2: Mapping Our World

2.1 Objectives
◗ Describe the difference between latitude and longitude.
◗ Explain why it is important to give a city’s complete coordinates when
describing its location.
◗ Explain why there are different time zones from one geographic area to the next

Latitude and Longitude

Lines of latitude and longitude are used to locate places on Earth.

Latitude
Maps are flat models of three-dimensional objects. For thousands of years
people have used maps to define borders and to find places. The map at the
beginning of this chapter was made in 1570 by Abraham Ortelius.
What do you notice about the size and shape of the continents? Today, more
information is available to create more accurate maps. The science of mapmaking
is called cartography
Cartographers use an imaginary grid of parallel lines to locate exact points
on Earth. In this grid, the equator horizontally circles Earth halfway between the
north and south poles. The equator separates Earth into two equal halves called
the northern hemisphere and the southern hemisphere.
 Lines on a map running parallel to the equator are called lines of latitude.
Latitude is the distance in degrees north or south of the equator as shown in
Figure 2.1. The equator, which serves as the reference point for latitude, is
numbered 0° latitude. The poles are each numbered 90° latitude. Latitude is thus
measured from 0° at the equator to 90° at the poles.

Locations north of the equator are referred to by degrees north latitude (N).
Locations south of the equator are referred to by degrees south latitude (S). For
example, Syracuse, New York, is located at 43° N, and Christchurch, New
Zealand, is located at 43° S.

Degrees of latitude
Each degree of latitude is equivalent to about 111 km on Earth’s surface.
How did cartographers determine this distance? Earth is a sphere and can be
divided into 360°. The circumference of Earth is about 40,000 km. To find the
distance of each degree of latitude, cartographers divided 40,000 km by 360°.
To locate positions on Earth more precisely, cartographers break down
degrees of latitude into 60 smaller units, called minutes. The symbol for a minute
is (΄). The actual distance on Earth’s surface of each minute of latitude is 1.85 km,
which is obtained by dividing 111 km by 60΄.
A minute of latitude can be further divided into seconds, which are
represented by the symbol (˝). Longitude is also divided into degrees, minutes,
and seconds.
1° = 60’ = 3600”
111 km= 1.85 km/min = 0.0005138888888 km/sec
Longitude
To locate positions in east and west directions, cartographers use lines of
longitude, also known as meridians. As shown in Figure 2.2, longitude is the
distance in degrees east or west of the prime meridian, which is the reference
point for longitude.

The prime meridian represents 0° longitude. Points west of the prime

meridian are numbered from 0° to 180° west longitude (W); points east of the
prime meridian are numbered from 0° to 180° east longitude (E).

Semicircles
Unlike lines of latitude, lines of longitude are not parallel. Instead, they are
large semicircles that extend vertically from pole to pole.
The line of longitude on the opposite side of Earth from the prime meridian
is the 180° meridian. There, east lines of longitude meet west lines of longitude.
This meridian is also known as the International Date Line.

Degrees of longitude
Degrees of latitude cover relatively consistent distances. The distances
covered by degrees of longitude, however, vary with location. As shown in Figure
2.2, lines of longitude converge at the poles into a point. Thus, one degree of
longitude varies from about 111 km at the equator to 0 km at the poles.
There are 360° of longitude (180° E ↔ 180° W) and 180° of latitude (90° N
↔ 90° S). Each degree can be broken into 60 minutes (’). Each minute can be
divided into 60 seconds (”). For finer accuracy, fractions of seconds given by a
decimal point are used.
why does a degree of longitude vary a distance with location while the degree of
latitude is the exact same everywhere on the earth?

A degree of longitude is about 111 kilometers (69 miles) at its widest. The
widest areas of longitude are near the Equator, where Earth bulges out. Because
of Earth's curvature, the actual distance of a degrees, minutes, and seconds of
longitude depends on its distance from the Equator. The greater the distance, the
shorter the length between meridians. All meridians meet at the North and South
Poles.

Using Coordinates
Both latitude and longitude are needed to locate positions on Earth
precisely.
For example, it is not sufficient to say that Charlotte, North Carolina, is located at
35°14´ N because that measurement includes any place on Earth located along
the 35°14´ line of north latitude. The same is true of the longitude of Charlotte;
80°50´ W could be any point along that longitude from pole to pole. To locate
Charlotte, use its complete coordinates — latitude and longitude — as shown in
Figure 2.3.
Time zones
Time zones are the functional basis of standard time and were introduced
in the late 19th century as railways connected places that had differing local
times.
Earth is divided into 24 time zones. Why 24? Earth takes about 24 hours to
rotate once on its axis. Thus, there are 24 times zones, each representing a
different hour. Because Earth is constantly spinning, time is always changing.
Each time zone is 15° wide, corresponding roughly to lines of longitude. To avoid
confusion, however, time zone boundaries have been adjusted in local areas so
that cities and towns are not split into different time zones.
For convenience, however, time-zone boundaries have been adjusted in
local areas. For example, some cities have moved the time-zone boundary so that
the entire city shares a time zone. As shown in Figure 2.4, there are six time zones
in the United States.

■ Figure 2.4 In most cases, each time zone represents a different hour.
However, there are some exceptions
 International Date Line
Each time you travel through a time zone, you gain or lose time until, at
some point, you gain or lose an entire day. The International Date Line, which is
180° meridian, serves as the transition line for calendar days. If you were traveling
west across the International Date Line, you would advance your calendar one
day. If you were traveling east, you would move your calendar back one day.

Reference:
Francisco Borrero • Frances Scelsi Hess • Juno Hsu Gerhard Kunze • Stephen A.
Leslie • Stephen Letro Michael Manga • Len Sharp • Theodore Snow • Dinah
Zike • National Geographic (2008) Earth Science: Geology, the
Environment, and the Universe. ISBN-13: 978-0-07-874636-9 ISBN-10: 0-
07-874636-1