A map topology creates topological relationships between the parts of features that are coincident, which allows you to simultaneously edit features that share geometry. You can create a map topology for point, line, or polygon layers from shapefiles or geodatabase feature classes. The features can be in one or more layers and have different layer types.
It is easy to create a map topology. You simply choose the layers to participate and set the cluster tolerance. In addition, if you click the Topology Edit tool without having an active topology, you are prompted to set up the topology.
Since a map topology is based on the layers in the map, layer visibility, such as definition queries and scale ranges, is respected. Only visible features are edited when you use the topology tools with a map topology. For example, you have a polygon layer that contains land uses and administrative boundaries but only want to update the land-use features. You can set a definition query on the layer to show the land-use features and hide the administrative boundaries. Since the administrative features are not visible on the map, they will not be updated when you perform topology edits.
On the other hand, in cases where features should be edited together, use caution when applying definition queries and turning off layers while making topological edits. For example, you have a layer of forest types with a definition query that displays only deciduous tree stands. The evergreen forest features are hidden from the map. When you edit, only the visible deciduous trees are updated, so the forests will no longer be coincident at edges where deciduous trees share boundaries with evergreens. You need to ensure all the features you want to edit together are visible so the correct topological coincidence is maintained.
- Click Select Topology on the Topology toolbar. The Select Topology dialog box appears.
- Check the layers that will participate in the map topology. All the layers in your current edit session that can participate in the map topology are listed on the dialog box. Layers representing annotation and dimension feature classes and feature classes that participate in a geometric network cannot be included in a map topology and are not listed.
- Optionally, click Options to view the cluster tolerance, which is the distance that defines how close together edges and vertices must be to be considered coincident. Generally, you should not change the default cluster tolerance because it is the minimum possible value. Increasing the cluster tolerance might cause more features to be snapped together and considered coincident, but this can reduce the spatial accuracy of your data and cause features to collapse or distort.
- Click OK.