GIS is a system of hardware and software used for storage,
retrieval, mapping, and analysis of geographic data. Practitioners also
regard the "total GIS" as including the operating personnel
and the data that go into the system, as well as the policies, procedures,
training and any other item or issue that effect the system.
Spatial features are stored in a coordinate system (latitude/longitude,
state plane, UTM, etc.), which references a particular place on the
earth. Descriptive attributes in tabular form are associated with spatial
features. Spatial data and associated attributes, in the same coordinate
system, can then be layered together for mapping and analysis. GIS can
be used for scientific investigations, resource management, and development
planning.
GIS differs from CAD and other graphical computer applications in that
all spatial data is geographically referenced to a map projection in
an earth coordinate system. For the most part, spatial data can be "re-projected"
from one coordinate system into another, thus data from various sources
can be brought together into a common database and integrated using
GIS software. Boundaries of spatial features should "register",
or align properly, when re-projected into the same coordinate system.
Another property of a GIS database is that it has "topology,"
which defines the spatial relationships between features. The fundamental
components of spatial data in a GIS are points, lines, polygons and
raster data. When topological relationships exist, you can perform analyses,
such as modeling the flow through connecting lines in a network, combining
adjacent polygons that have similar characteristics, and overlaying
geographic features."
