Geography Reference
In-Depth Information
attribute transformation begins only here. Various operations, logical and
mathematical, are used to transform attributes and relate them—for exam-
ple, evaluating soil type and soil moisture to determine crop suitability. Ras-
ter GI performs these attribute transformation as the overlay transforma-
tion, assuming both raster data sets use the same raster size and origin point
(otherwise some complex geometric transformations must first take place).
Chapter 14 covers these issues and the overlay operation in more detail.
Summary
This chapter examined GI representation types and transformations. GI rep-
resentation types are the formats available for GI: positions, networks, and
fields. Positions and networks rely on vector data formats; fields rely on ras-
ter data formats. Positional GI is stored in a GIS as points, lines, or areas
(also known as polygons), most often following the georelational model that
uses topology. Networks also use these data formats, but areas are of very
limited use in a network. Points, called nodes in networks, are much more
important.
Transformations are operations on GI representation types that change
the information content. A buffer transforms a point through a distance
measure into an impacted area.
In-Depth
Some Applications and Geographic
Information Representation Types
Application
GI Representation Type
Data Types
Water pollution
Raster
Water characteristics, models of
pollutant diffusion
Vehicle routing
Network
Roads and highways
Biotope conservation
Position
Location and types of biotopes,
landuse and landcover
In-Depth
Topology
A modern branch of mathematics with great impacts in many fields, topology
has been an important inf luence on the development of GI. Topology was
introduced by one of history's greatest mathematicians, Leonard Euler, in
1736 when he published a paper on how to solve a puzzle that had perplexed
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