Introduction to Topology Rules: Within and between Topological Rules (Especially for GATE-Geospatial 2022)

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A GIS topology is a set of rules and behaviors that model how points, lines, and polygons share coincident geometry.

A group of instruction to the geo-database defining the permissible relationships of features within a given feature class or between features in two different feature classes.

Many topology rules can be imposed on features in a geodatabase. A well-designed geodatabase will have only those topology rules that define key spatial relationships needed by an organization.

How to Check Topology Error in QGIS

Within and between Topological Rules

They are of two kinds

  • Some rules are for within a feature class.
  • Some rules are for between two feature classes.

For example,

  • Adjacent features, such as two counties, will have a common boundary between them. They share this edge.
  • The set of county polygons within each state must completely cover the state polygon and share edges with the state boundary.


The following list shows some examples of where topology rules can be defined for real world features in a vector map:

  • Area edges of a municipality map must not overlap.
  • Area edges of a municipality map must not have gaps.
  • Polygons showing property boundaries must be closed. Undershoots or overshoots of the border lines are not allowed.
  • Contour lines in a vector line layer must not intersect.

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