# About editing shared geometry

To work with shared geometry, you will need to have a map or geodatabase topology on your data. Then, you can select edges and nodes that may be shared by more than one feature, modify them, and have all the features that share the node or edge be updated.

The Topology Edit tool allows you to select and modify edges and nodes that may be shared by more than one feature. It also allows you to select and move the individual vertices that define the shape of edges. When you move vertices, edges, or nodes with the Topology Edit tool, all the features that share the node or edge are updated.

## Editing shared edges

When editing topological features, you often have a choice of several ways of doing a particular task. For example, suppose you manage a forest and there are two polygon feature classes, Forest and Stands, in your forest dataset. The two images below show the forest and stand polygons.

Forest polygon

Stands polygons

The Forest and Stands polygons are related by three topology rules: Stands must not overlap, Forest must cover Stands, and Stands must cover Forest. These rules prevent Stands polygons from overlapping, since no area can be in two stands at once. They also prevent stands from extending outside the official boundary of the whole forest or the forest boundary from covering an area not in a stand.

Suppose you are editing the Stands feature class and need to change the boundary between two of the stands. You could start editing; use the Topology Edit tool to select the shared edge; double-click the edge to edit its vertices; then add, remove, and move vertices along that edge to shape it to fit the new boundary.

You could also use the Topology Edit tool to modify edges shared by the Stands and Forest polygons. For example, suppose the actual boundary of the forest has been determined to be 150 meters east and 20 meters north of the corner where two stand features meet at the edge of the forest. You could use the Topology Edit tool to select the topology node at this intersection of features and move it to the correct location, either manually or by right-clicking the node, clicking Move, and entering the delta x,y value. The stand and forest polygons will both have their boundaries updated.

## Modifying and reshaping shared edges

In addition to editing topology elements with the Topology Edit tool, you can also modify and reshape a selected topology edge using an edit sketch. The Modify Edge and Reshape Edge tools allow all features that share the edge to be updated at the same time.

Modify Edge takes the selected edge and makes an edit sketch from it. You can use the standard editing tools to insert, delete, or move the vertices that make up the edge, although you cannot move the endpoints when modifying edges. With the Reshape Edge tool, you can use the basic editing tools to create a new line to replace an existing edge line.

## Using regular editing tools to edit features in a topology

You can also use the regular editing tools to edit individual features that participate in a topology. When you edit topologically related features using the regular editing tools, you are only modifying one feature at a time. If this feature shares geometry with other features, the shared geometry is not updated. If the edits create a violation of the geodatabase topology rules, you can use the Error Inspector to find the error and the Fix Topology Error tool to fix the error. The Fix Topology Error tool allows you to right-click an error and choose which fix to use for the error.

For example, if you use the Reshape Feature tool to reshape a selected polygon's border, only that feature will be updated. Since the border of the adjacent polygon was not updated at the same time, you can end up with overlapping polygons. 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.

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

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

5/6/2011