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Vector Data TopologyContents |
An important concept when using the vector data model is topology. Topology is a mathematical method used to define spatial relationships that allows a GIS to structure data based on the principle of feature adjacency and feature connectivity. The topological data structure determines how and where points and lines connect. The order of connectivity defines the shape of an arc or a polygon. Without a topologic data structure, the data manipulation and analysis function of a GIS would not be possible.
In a topological model, a polygon is defined as by a series of arcs. Arcs begin and end at nodes, which occur where two or more arcs meet. Each arc is defined by a series of coordinate pairs, each with a start and end node. GIS software stores topological definitions in three tables representing the different features, i.e. point, line, area. The node table stores information about the nodes and arcs that are connected to it. The arc table contains topological information about the arcs, including start and end nodes and the polygons to the right and left of the arc. The polygon table defines the arcs that make up each ploygon.
One of the important examples of how a GIS can be used to model real world events is the ability to model networks. There are many networks in geographical data, such as water courses and road networks. Network analysis uses topological modelling to analyse the potential flow around these networks, a useful ability in flood analysis or route finding. It can only do this if the data has correct network topology.
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Information about this article
Short title: Topology
Description: none
Expertise level: beginner
Author: Greg Reed
Approval status: approved
Approved by: Greg Reed
Last change: 2010-4-22
Subsection of: Fundamentals of Geographic Information Systems
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