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Creating a topology

Building Geodatabases

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In this exercise, you will see how to create a geodatabase topology. A geodatabase topology allows you to specify rules that control the spatial relationships of features in a dataset. There are a variety of topology rules that you can apply to your data, depending on your organization’s requirements. You will only see two topology rules applied to this dataset.

You’ll see how to create a topology to regulate two types of spatial relationships in this dataset. The first is that parcels should not overlap, and the second is that parcels that have been classified as residential must fall within blocks that are also classified as residential.

Ranks allow you to ensure that more accurately collected features are not snapped to the position of less accurately collected ones when the topology is validated. For example, if you were including a feature class that was collected using a survey grade global positioning system (GPS) unit and a feature class digitized from a 1:1,000,000- scale source map in the same topology, you might assign the GPS feature class a rank of 1 and the 1:1,000,000-scale source feature class a rank of 5. If you were to validate the topology, parts of features that fell within the cluster tolerance would snap together, with the less accurate ones moving to the location of the more accurate ones. The GPS features would not be moved to the position of the 1:1,000,000-scale features. You can assign up to 50 different ranks, with 1 being the highest rank. In this topology, you will assume that all the feature classes are based on equally accurate data, so you will not assign more than one rank. Parcels and Blocks have equivalent levels of accuracy, since the Blocks feature class was derived from the parcel features.

Topology rules allow you to define the permissible spatial relationships of features within and between feature classes that participate in the topology. Landownership parcels are usually not allowed to overlap each other. You will add a rule to prevent your parcel features from overlapping each other.

After the topology is created, you have the opportunity to validate it. You do not need to validate the topology immediately after creating it. Depending on your data and your work flow, it may make sense to assign different areas to data editors to validate and edit within ArcMap.

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