About editing geometric network features(ArcInfo and ArcEditor only)
Last modified July 23, 2009
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NOTE: While network features can be both created and edited in ArcInfo and ArcEditor, they are read-only in ArcView.
Topological connectivity in a network feature class is based on geometric coincidence. If a junction is added along an edge, or one edge is added along another edge, they will become topologically connected to one another.
By using the ArcMap snapping environment, you can create new edge and junction features while maintaining network connectivity on the fly. The ArcMap snapping functionality will guarantee geometric coincidence when adding new network features along existing network features.
It is generally critical to maintain connectivity since your tracing and other networking tasks won't work as expected without it.
Since connectivity is based on geometric coincidence, establishing connectivity with coincident features will be indeterminate. For example, if a junction is added along two coincident edges, the junction may connect to either edge. As such, coincident features are not supported within the geometric network.
An edge in a geometric network can be either simple or complex. A simple edge in a geometric network has a 1–1 relationship with edge elements in the logical network. A complex edge has a 1–M relationship with edge elements in the logical network. So one complex edge in the geometric network can represent multiple edges in the logical network.
If you snap a junction or edge along a simple edge, then the edge being snapped to is split both in the logical network and in the geometric network, giving you two edge features. If you snap a junction or an edge along a complex edge, then that edge is split in the logical network but remains a single feature in the geometric network. It will remain a single feature; however, a new vertex is created at the point where the new junction or edge connects to it.
When you snap an edge to another edge where there is no junction, a junction is automatically inserted to establish connectivity. If a default junction type has been specified as part of the connectivity rules for the network, that default junction type is used. If there is no edge-edge rule between these edge types, an orphan junction is inserted, which is stored in the <network>_Junction feature class.
Similarly, if you create a new edge in the network that is not snapped to an existing junction or edge at both ends, a junction is automatically created and connected to the free end of the new edge. If there is a connectivity rule in place that defines a default junction type for the type of edge that is being added, that default junction type is the junction that is added to the free end of the new feature. If an edge type does not have a default junction type associated with it through a connectivity rule, then an orphan junction is inserted, which is stored in the <network>_Junction feature class.
Learn more about connectivity rules.
When you snap a junction to an existing orphan junction, the orphan junction is subsumed by the new junction. That is, the orphan junction is deleted from the network and the new junction is inserted in its place. All network connectivity is maintained. Orphan junctions cannot subsume other orphan junctions. When a junction is snapped to another junction other than an orphan junction, subsumption does not occur and the newly added junction is not connected.
When you create a new edge feature in the network that has an end that does not connect to anything, and there is not a connectivity rule stating what type of junction to put at its free end, the network orphan junction type is inserted. This orphan junction can be replaced by snapping another junction to it.
When a network edge or junction is moved, the network features to which it is connected respond by stretching and adjusting themselves to maintain connectivity. When you move a network feature and snap it to another network feature, the features may become connected (as illustrated in the following section, Connectivity models).
Edit operations that involve adding, deleting, moving, and subsuming network features can all affect the connectivity of a geometric network. Each type of operation may or may not create connectivity, depending on the type of network features involved. If connectivity is not created, it can be established by using the Connect command.
The following set of diagrams illustrates various editing scenarios and their resulting connectivity or lack thereof. In these diagrams, use the key below to identify what types of features are illustrated in each scenario:
Connectivity between network features is maintained on the fly as you create, delete, and modify network features. In some circumstances, the association between certain network features and their logical elements may become out of sync. This can happen, for example, when using a custom tool that does not correctly handle aborting edit operations.
This kind of network inconsistency is usually localized to a collection of features in the network. You will be able to see what features have inconsistent connectivity in three ways:
Connectivity is established for new network features based on geometric coincidence. When you add or move a feature in a network, each feature class in the network must be analyzed so that connectivity can be established. Performing a spatial query against each network class will determine if the new feature or moved feature is coincident with other network features at any point.
If the network is in an ArcSDE geodatabase, then analyzing for connectivity requires a number of spatial queries against the server. Using the map cache can make your edits many times faster than they would be without the cache, and it does not require as much of the server.
Learn more about the map cache.