Validating a topology
Once you have created a topology and loaded data, at any time, you can run a validation against the feature class contents of the topology. Validate performs the following processing tasks:
- Cracking and clustering of feature vertices to find features that share geometry (have common coordinates)
- Inserting common coordinate vertices into features that share geometry
- Running a set of integrity checks to identify any violations of the rules that have been defined for the topology
- Creating an error log of potential topological errors in your feature dataset
Once a new topology has been validated, subsequent edits are noted with dirty areas that identify subsets of your feature dataset that require revalidation. This saves time and improves performance, because only the areas that need to be revalidated can be processed.
Ways to validate a topology
- You can validate a topology in the Catalog window or ArcCatalog by right-clicking the topology in the tree view and clicking Validate.
- You can validate a topology from the Topology toolbar during editing.
- The Validate Topology geoprocessing tool can be used to validate a topology as part of an automated workflow. Scripts can be useful for automating a series of tasks and for building repeatable workflows.
Tips on topology validation
- You have the freedom to choose when and how often you validate your topology. Typically, each topology must be validated in its entirety only once. All other validations will only revalidate dirty areas where changes have occurred.
- ArcGIS will automatically track dirty areas for you as you edit your data and if you change your topology definition. When you validate your topology, ArcGIS will automatically know the dirty areas that have to be validated.
- How often should you validate your topology? It is best to revalidate your topology after you have edited your feature dataset. You may also choose to validate portions of your dataset during editing so that you can find and fix errors during the editing process.
- If you change your topology definition, you may need to revalidate your topology. For example, if you change the topology rule set or the coordinate ranks, the whole topology will be flagged as dirty and will be revalidated the next time you run validation.
- Revalidating your topology does not mean that cluster processing will cause your coordinates to move more in each subsequent validation. Once you have clustered your coordinates in the initial validation, they will not move in subsequent validations unless new geometries have been added that fall within the x,y tolerance of existing features (for example, when you connect a new road to a street network, split a parcel, and so forth). In these cases, only the changed areas where vertices fall within the cluster tolerance of other features will be clustered and, therefore, potentially adjusted.
- The feature classes that participate in a topology are always available for use within ArcGIS regardless of whether or not the topology has been recently validated. If the topology has not been validated, some of your features may not adhere to your integrity rules. However, they are available for use—with or without errors.
- When you validate your topology, it generates an error report so you can be aware of issues and have the opportunity to repair serious errors. In this way, topology helps you know about the integrity of your datasets and their suitability for use in various applications.