Laboratory Manual for Introductory Geology 4e

More sophisticated grid systems are used for more precise locations. Maps published
by the USGS use three different grid systems: latitude/longitude, the Universal
Transverse Mercator (UTM) grid, and for most states, the Public Land Survey (or
Township and Range) System. The UTM grid is least familiar to Americans but is
used extensively in the rest of the world.
8.3.1a Latitude and Longitude The latitude/longitude grid is based on location
north or south of the equator and east or west of the prime meridian, a line that
passes through the Royal Observatory in Greenwich, England (FIG. 8.3). A parallel
of latitude connects all points that are the same angular distance north or south of
the equator. The maximum value for latitude is therefore 90° N or 90° S (the North
and South Poles, respectively). A meridian of longitude connects all points that are the
FIGURE 8.3 The latitude/longitude grid.
90° N latitude
North Pole
60° N latitude
90° W longitude
Prime meridian
0° E or W longitude
30° N latitude
30°
30°
Equator
60°
Equator
30° S latitude
60° S latitude
75° W longitude
90° E longitude
90° S latitude
South Pole
(a) Latitude is measured in degrees north or
south of the equator.
60° W longitude
(b) Longitude is measured in degrees east or west of the
prime meridian (Greenwich, England).
45° N latitude,
15° E longitude
0° N or S latitude,
0° E or W longitude
30° S latitude,
75° W longitude
(c) Locating points using the grid.
202 CHAPTER 8 STUDYING THE EARTH’S LANDFORMS: MAPS AND OTHER TOOLS