Geoscience Reference
In-Depth Information
be described in terms of its position north or south of the
Equator and east or west of the Prime Meridian. Imagine, for
example, that you wanted to find Washington, D.C., in the grid;
Washington is located at 39° N (latitude), 77° W (longitude). To
see how you would locate Washington within the grid, examine
Figure 2.8 again. Beginning with latitude, find the 38th parallel
north of the Equator to identify the location in the Northern
Hemisphere. Once this is accomplished, locate the Prime
Meridian and arc west to the 77th meridian. The intersection
of the 38th parallel and the 77th meridian is the position of
Washington, D.C. Notice that you can first find the latitude or
you can first find the longitude; the order does not matter, as
you wind up at the same place either way. However, remember
that by convention the latitude of a location is always specified
before the longitude is given.
80 N
8 8 N
8
60 N
6
6 6
6 6
6
6
6
Washington, D.C.
4 0 N
7
39
3 9
3
20 N
2 20 N
E
W
7 77
N
N
0
Human Interactions: The United States
Public Land Survey
The preceding discussion about latitude and longitude revolved
around the global grid system used to determine location on
Earth. In addition to this grid system, the United States also
uses another form of grid network that is based on the cardinal
directions (north, south, east, west) to organize the landscape
in association with property ownership. Have you ever flown
over the central part of the United States and noticed that the
landscape is systematically organized into hundreds of giant
squares? This grid is part of the United States Public Land
Survey system (USPLS) and is the framework that surveyors
used to survey the majority of the country during the era of
westward expansion in the 1800s.
The USPLS was originally proposed by Thomas Jefferson
and was implemented shortly after the Revolutionary War in
the late 1780s to survey the large tracts of land then avail-
able for settlement west of the original 13 colonies. Prior to
the establishment of the USPLS system, landscape survey in
the colonies had followed the metes and bounds system, which
was based largely on the location of landmarks such as trees,
20 W
2 2 2 2
W
S
S
Figure 2.8 Determining latitude and longitude of Washington,
D.C. Using the grid network, we can locate Washington, D.C.,
at approximately 39° N, 77° W.
A primary difference between longitude and latitude is that
while lines of latitude are always parallel to one another, lines
of longitude converge at the poles (Figure 2.7a). Thus, degrees
of longitude are about 110 km (69 mi) apart at the Equator and
progressively shorten in distance until they meet at the poles.
As with latitude, a common misconception about longitude is
that meridians are used to determine location north and south
because that is the direction in which the semicircle outlines
extend. Instead, remember that longitude determines location
east and west of the Prime Meridian.
Using the Geographic Grid
Now that the two grid components of latitude and longitude are
in place, they can be overlain to form a complete grid network
that encompasses Earth (Figure 2.8). Thus, any location can
United States Public Land Survey The primary way that
land is subdivided in the United States by using a grid system
based on the four cardinal directions.
www.wiley.com/college/arbogast
Using the Geographic Grid
In order to help you fully comprehend how the complete geo-
graphic grid works, view the animation Using the Geographic
Grid . In this simulation you will be able to select a number of
places on Earth and determine their latitude and longitude. This,
in turn, should help you better understand where locations are
in physical space. Once you complete the exercise, be sure to
answer the questions at the end to test your understanding of
the geographic grid.
 
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