Locational and Coordinate Systems - A Primer of GIS: Fundamental Geographic and Cartographic Concepts - page 100

PRINCIPLES OF GI AND CARTOGRAPHY Locational and Coordinate Systems

Chapter 5

Locational and Coordinate Systems

Applying Projections

Projections make it possible to create maps and two-dimensional geographic
information using locational and coordinate systems to create common ref-
erence systems. Reference systems are used by national governments, state
and provincial governments, local governments, the military, nonprofits,
and businesses around the world. They make it possible for many people to
work with geographic information and maps without following the specifics
of projections. Their widespread use has made them crucial references for
many activities. Common reference systems simplify the recording of the
location of things and events and make it possible to combine information
from different sources and to verify any distortions of positional measure-
ments.
A commonly used locational or coordinate system helps greatly to mini-
mize distortion. Accordingly, and just as with projections, working with geo-
graphic information or maps can require knowing which locational or coor-
dinate system is used. Different locational or coordinate systems can record
the location of things and events from the same area at different places.
Even if they seem to overlap when drawn together, varying degrees of differ-
ences can lead to subtle or significant errors that can impact analysis.
Locational systems are different from coordinate systems. Although the
terms are often used interchangeably, it is important to recognize a key dif-
ference. A locational system can be referenced to a projection; a coordinate
system must be referenced to a projection and the reference model of the
earth's shape and size. Usually this is known as a datum . Locational systems,
generally with orthogonal coordinates, are only valid for particular data or
possibly even with one map and may not have any connection to other
locational and coordinate systems.
In this chapter you will read about the creation, history, and use of

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