Global Positioning System Reference
In-Depth Information
Geographic Information Systems (GIS)
Geographic information systems are a product of the computer age, and
from the 1970s and 1980s on, they have revolutionized the ancient science
and art of mapmaking. Globalization has led to a number of di√erent
universal spatial reference systems, analogous to the world clock in time-
keeping. Thus, there is the International Terrestrial Reference System and
the World Geodetic System. Such systems enable di√erent countries and
data sources to merge and exchange data, thus greatly expanding the infor-
mation that is available for mapmakers way beyond what was possible to
present on maps of days gone by. A GIS takes advantage of this plethora of
new data, and of the computational power and large memory of digital
computers, to capture, store, and manipulate spatial data so that it can be
presented in the best manner for di√erent applications.
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GIS is used widely in scientific research, resource management and
ecology, archaeology, infrastructure assessment and development, demo-
graphic studies, disaster management, the spread and control of disease
and pollution, and many other fields. An ecologist might use GIS to exam-
ine the retreat or advance of vegetation in a Third World drought zone or a
city green belt. A town planner might use GIS to assess the infrastructure
requirements and population dynamics associated with a proposed large
shopping mall development. Wherever layers of information interact, GIS
finds an application.
This idea of layering spatial data is central to GIS, and the ability of
digital computers to strip o√ or add layers to a map is a key feature. For
example, the land on which a town lies can be represented by topographi-
cal data, complete with contour lines, rivers, and perhaps geological infor-
mation. The same area might be represented by a layer of data containing
streets and pathways of di√erent types, perhaps with tra≈c lights and one-
way travel information. Buildings may constitute a third layer, with infor-
mation about public facilities, stores, hospitals, and so on. Other layers
may be added as new data become available. Layers of data can be selected
for certain applications and printed on a map, or information from all
layers may be presented about a specific location (thus, planning for a new
building will require geological and street plan information, but perhaps
not contour data).
13. A nontechnical summary of GIS is that of Raju (2004).
