Laboratory Manual for Introductory Geology 4e

FIGURE 8.2 Three common map projections and their different views of the world. The equator is indicated in each
projection by a red line.
(a) Orthographic. (b) Mercator. (c) Uninterrupted sinusoidal.
TABLE 8.1 The strengths and weaknesses of three common map projections
Strengths
Weaknesses
Comments
Uses
Orthographic Mercator Uninterrupted sinusoidal
Directions between points are
preserved. East–west distances
are accurate.
Shapes and areas are distorted,
especially near the edge of the
projection. Distances other than in
east–west direction are distorted.
Perspective view is similar to view
of a globe from a great distance.
Note accurate representation of
size of Greenland compared with
the Mercator projection.
Often used to provide context
for images of the Earth taken
from space.
Accurate near the equator.
Directions preserved in most
areas.
Severe shape and area
distortions away from the
equator. Useless for north and
south polar areas.
Note vastly distorted polar
areas of Greenland (shown
much more accurately on
the other projections) and
Antarctica.
Nautical navigation charts,
because point-to-point
directions are accurate.
Areas of continents are represented
accurately.
Scale is constant only along a central north–
south line and the equator, and changes
elsewhere. Shapes of features distant from
these reference lines are distorted.
Note that the area of Greenland (much
smaller than Africa or South America) is
portrayed accurately compared with the
Mercator projection.
Commonly used for features elongated
north–south (e.g., maps of Africa and
South America).
projections are shown in FIGURE 8.2, and TABLE 8.1 indicates what they distort and
for what purposes they are best used.
8.3 Map Elements
An accurate portrayal of the Earth’s surface must contain three basic elements:
(1) location, a way to show precisely where on the planet a feature is; (2) the distance
between features; and (3) an accurate depiction of the directions between
features. In many instances, it is also important to know the elevations of hilltops
and other features and the steepness of the slopes in mountains, hills, and valleys.
8.3.1 Map Element 1: Location
Road maps and atlases use a simple grid system to locate cities and towns; for example,
Chicago is in grid square A8. Many other places may be in the same grid square,
but this location is good enough for someone driving to Chicago from Los Angeles.
8.3 MAP ELEMENTS
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