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  In mathematics, a property that is invariant under spatial distortion. For example, if a line is drawn on a rubber sheet, it is impossible to stretch the sheet so as to make the line into a point; thus the property of being a line, rather than a point (a one-dimensional object rather than a zero-dimensional object) is a topological property. In geographical information systems (GIS) the term applies similarly to those aspects of a database that survive geometric distortion of objects; such aspects include adjacency and connectivity between objects, and the distinction between points, lines and areas. One major distinction between GIS and much computer-assisted design (CAD) and computer-assisted cartography software is the ability to handle topology, since topological properties such as relationships between objects are central to many forms of spatial analysis, and thus to the role of GIS in implementing such methods.

In digitizing a map, it is virtually impossible to ensure that there is perfect closure between the two ends of a loop representing an area\'s boundary, or between two lines that should meet at a point. Software is used to detect near-intersections, and to make perfect closures. Because this process results in a transformation of lines into perfectly closed areas it is referred to loosely in GIS as \'building topology\' (e.g. Demers, 1997, p. 109). (MG)

References DeMers, M.N. 1997: Fundamentals of geographic information systems. New York: Wiley.



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