introduction 9
is recent. On early maps, the data stored were usually locational. Positions of islands,
routes, or records of boundaries for the tax collector are examples of this type of
early data storage. Maps still perform this function, but the kinds of data stored have
expanded and sometimes the method of storage has changed. For example, boundary
lines may be recorded and stored in digital form and printed on demand.
Maps are, by their very nature, spatial representations. That is, they show posi-
tions in space. They are uniquely suited therefore to portray features of the earth’s
surface (for terrestrial maps) or to show the
spatial relationships of features to one
another. No other device can do this as well as a map. Text, tables, and even graphs
do not possess the spatial component and do not allow readers to see distributional
patterns.
Because of their ability to show spatial relationships, maps are used as analytical
and explanatory tools. Some geographic patterns cannot be recognized until they are
presented in map form; therefore, maps are often made to aid a researcher in identify-
ing or correlating
distribution patterns, that is, visualizing data.
Finally, maps are used to present or communicate information to an audience,
which might be readers of a report, students studying a textbook, a shopper looking
at a “you are here”
map of a mall, or a hiker checking a route at a trail head.
limitations of maps
In spite of their usefulness, maps have limitations. Many map readers are not aware
of these limits (and the appearance of some published maps shows that not even all
mapmakers are aware of these limitations). Part of the problem is that people often
assume that a map shows everything, like a photograph. A photograph taken from
the air from low-flying aircraft shows whatever is in view: houses, streets, cars, the
family dog, and even laundry drying in the backyard. Figure 1.6 shows the port of
Long Beach with boats and their wakes in addition to docks and buildings.
Maps are not photographs. This seems an obvious, even simplistic, statement,
but the distinction is important. Photographs are not selective except through the
inherent selection of
resolution, that is, the size of objects large enough to be seen.
This varies with the height of the aircraft or satellite and the capabilities of its sensor.
Maps are graphic representations, which by their very nature are selective and sym-
bolic, that is,
generalized. Maps do not show every bit of available information. To do
so would clutter the map with information that isn’t relevant to the theme or topic of
the map. It would obscure the message. Symbols substitute for images of objects. The
map in Figure 1.7 shows the same area as the picture in Figure 1.6.
While selection is vital, it also acts as a major limiting factor on maps. Although
some “missing” facts may be inferred from other information, normally one cannot
read into a map information that is not shown. For example, one cannot determine
the exact nature of terrain from a map that shows the pattern and amounts of rain-
fall, although some educated guesses can be made.
Selection
also involves bias, a subject that has been
of interest to researchers
in the past 30 years. The decision of what to include on a map depends on many
objective factors, but also on subjective factors, such as what the cartographer, the
mapping agency, or the client want to show and emphasize. All maps are biased to
some extent. This does not mean they are therefore evil or incorrect, but one should
