introduction 11
be aware of this fact when using or making a map. Selection is discussed more fully
in Chapter 5.
A second limitation is imposed by
scale. In part, maps are selective because of
scale considerations. Maps are drawn smaller than reality, and in this process of scal-
ing down, some detail is necessarily lost. The greater the reduction from actual size,
the more generalized the information becomes.
A third limiting factor results from the inescapable fact that the earth is spheri-
cal and maps are flat. It is not possible to transform the spherical shape of the earth
onto a flat map without some distortion somewhere on the map. However, it is pos-
sible to minimize distortion or to confine it to a part of the map away from the area
of primary interest. The process of transforming the earth’s grid to a plane is called
projection.
Finally, as we have seen, maps are limited to showing
spatial relationships and
characteristics such as distance, direction, position, angle, and area. Maps cannot
effectively illustrate ideas and concepts that lack a spatial component. Sometimes a
word is worth a thousand pictures. The mapmaker must decide whether a map is the
most appropriate medium for communicating an idea.
The mapmaker has a responsibility to the map user to create a map that mini-
mizes the map’s limitations or uses them to enhance communication. This subject is
treated in detail in later chapters.
the Power of maps
Maps are powerful tools. They are often accepted at face value and their veracity is
seldom questioned by users. Whereas a reader might question the sources of a table,
or of a text, he or she often assumes a map to be accurate until it is proven otherwise.
This is especially the case with GIS maps because a computer-created map conveys
a sense of great accuracy. Blithly assuming maps to be
accurate can have serious
consequences. Maps are used in decision making, whether deciding which route to
take, which county should receive the most money, or where a boundary line should
be drawn.
In the worst-case scenario, maps can and do kill. The most famous recent exam-
ple is the 1998 tragedy of 20 deaths in Italy when a low-flying jet plane cut the cables
of a ski gondola that was not shown on the pilots’ map.
Other examples include
deaths by friendly fire from using outdated maps and plane crashes into towers not
shown on a map.
Often, the problem is using a map for which it was not designed, such as using
a road map to decide election districts. However, a major problem for our purposes
is failing to design a map for it’s intended purpose. A ship’s navigator isn’t interested
in roads on land, he or she is concerned with possible hazards to navigation. Leaving
out a road will cause no problems, but leaving out a submerged hazard can lead to
tragedy.
Maps are used in planning, real estate, and government that influence decisions
on location of industries and developments, where one buys a home, and where con-
gressional districts are drawn. Maps are also available
online that show housing
values, taxes paid (or unpaid), the size
of the house, the
number of rooms, and when
the house was last sold. This information is in the public record, but its availability to
12
MaP Design
anyone with an Internet connection anywhere in the world raises concerns. Thus, we
must consider the social impact of the maps we make and the ethics of the field. This
will be a recurring theme in this book.
