Geoscience Reference
In-Depth Information
The rest of the chapter is organized as follows. In the following section we
present the principles of GIS and give an overview of their basic functions. We then
discuss the main elements of location science and the various types of models arising
in the literature. In the next section we analyze some of the possible connections
between location science and GIS and discuss how the interaction between the
two disciplines has developed over the years. We then present some applications
exploiting this interaction and finish with some conclusions and further research
suggestions.
19.2
Principles of GIS
Different definitions have been proposed for describing GIS by single authors or
scientific and institutional organizations (Chrisman
1999
). In broad terms GIS are
information systems that integrate, store, edit, analyze, share and display geographic
information as well as non-spatial information for supporting decision making. In
the practical use of the term, it came to indicate a technology as well as a tool or a
way of data acquisition, management, manipulation, analysis and display.
Data lies at the core of any GIS tool. Obtaining accurate, up to date and reliable
data is often more difficult or more costly than acquiring a GIS tool itself. Typically,
GIS store information as a collection of thematic layers that are linked together by
geography. In practical terms, GIS combine
spatial data
, namely data that is in some
way referenced to locations on the earth and
attribute data
that can be generally
defined as additional information about each of the spatial features. Attribute data is
typically represented in tabular format. For instance, in a GIS implementation of a
facility location problem, spatial data may refer to the coordinates of the customers
and the candidate locations for the facilities and attribute data may refer to the
demand of each customer or the fixed cost of each candidate location. Other types of
data such as image or multimedia are also becoming relevant in GIS following the
rapid advances in technology. Documentation of GIS datasets is known as
metadata
.
Metadata contains such information as the coordinate system, when the data was
created, last updated, etc.
Spatial data is represented using a vector or raster/image format. The vector data
model implies the use of discrete line segments (vectors) and points to represent
geographic features. It can represent points, lines and areas. Each point or vertex
consists of an X coordinate and a Y coordinate. An area is represented as a sequence
of vectors where each vector starts where the previous one ends and where the last
vector ends where the beginning vector of the sequence starts, thus enclosing the
area in question. The raster data model divides the study area into a regular grid
of cells with each cell containing a single value reflecting the dominant property
or attribute within the cell. Since most data is captured in a vector format, e.g.,
by digitizing, data must be converted to the raster structure. This is called
vector-
raster conversion
. Most GIS software allows the user to define the raster cell size for
vector-raster conversion. It is imperative that the original data scale, e.g., accuracy,
