Three Steps in Editing Using Topology Rules (Especially for GATE-Geospatial 2022)

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The geodatabase data model has a total of 25 topology rules for point, line, and area features. Editing with a topology rule involves three basic steps.

  • Create a new topology
  • Validation of topology
  • Fix topology errors

1. Creates a New Topology

The first step creates a new topology by defining the participating feature classes, the ranks for each feature class, the topology rules, and a cluster tolerance. Suppose a topology includes two feature classes of soil and vegetation cover. If the soil feature class is deemed to be the more accurate of the two, it is assigned a higher rank, thus ensuring that its polygon boundaries will not be moved as much as the other feature class.

2. Validation of Topology

The second step is validation of topology. This step evaluates the topology rule and creates errors indicating those features that have violated the topology rule. Validation of topology is like “cleaning” coverage, and the cluster tolerance plays the role of the fuzzy tolerance. Validation results are saved into a topology layer, which is used in the third step for fixing errors and for accepting errors as exceptions.

3. Fixing Topological Errors

The geodatabase data model provides a set of tools for fixing topological errors. For example, if the study area boundaries from two participating feature classes are not coincident and create small polygons between them, we can opt to subtract these polygons, or create new polygons, or modify their boundaries until they are coincident.

Such an error will be discovered when you validate your topology edits. You can then use the fix topology error tool to merge the error with one of the features and remove the overlap.

This Figure Shows Error Tool to Merge the Error

When the topology is validated, the overlapping area is discovered as a topology error.

This Figure Shows the Overlap is a Tolology Error

The overlap is removed by applying the Merge topology error fix. The overlap is merged into feature 1, and the feature 1 and 2 now are adjacent and share a border.

This Diagram Shows Overlap is Removed by Applying the Merge …

Repetition of Steps

As with the editing of coverages, the steps of creating a topology, validating the topology rule, and fixing topological errors may have to be repeated before we are satisfied with the topological accuracy of a feature class or of the match between two or more feature classes.

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