Understand network elements

Available with Network Analyst license.

Network datasets are composed of network elements. Network elements are generated from the source features used to create the network dataset. The geometry of the source features helps establish connectivity. In addition, network elements have attributes that control navigation over the network.

The following are the three types of network elements:

  • Edges—Connect to other elements (junctions) and are the links over which agents travel.
  • Junctions—Connect edges and facilitate navigation from one edge to another.
  • Turns—Store information that can affect movement between two or more edges.
Source Settings tab

Edges and junctions form the basic structure of a network. Connectivity in a network deals with connecting edges and junctions to each other. Turns are optional elements that store information about a particular turning movement; for instance, a left turn is restricted from one particular edge to another.

Network sources

There are three types of network sources that can participate in the creation of a network dataset, as follows:

  • Edge feature sources—Line feature classes participate as edge feature sources.
  • Junction feature sources—Point feature classes can participate as junction feature sources, but multipoint feature classes cannot.
  • Turn feature sources—Turn feature classes participate as turn feature sources in a network. A turn feature source models a subset of possible transitions between edge elements during navigation.

Each feature class that participates in a network as a source generates elements based on its assigned role. For example, a line feature class is used as a source for edge elements, and a point feature class is used to generate junction elements. Turn elements are created from a turn feature class. The generated junction, edge, and turn elements form the underlying graph, which is the network.

Geometric and utility network feature classes cannot participate as network dataset sources because they are actively linked to a geometric or utility network. Feature classes that participate as a source in a network dataset can participate in a topology. Source feature classes cannot have 64-bit object identifier (OID) fields.

Consider the example of a simple transportation network and the sources that participate in its creation. This network has a streets feature class that can act as an edge source, a street intersections feature class acting as a junction source, additional line feature classes that act as edges (rail lines and bus routes), and point feature classes that act as junctions (rail stations and bus stations).

Simple transportation network features

All feature classes that reside in the feature dataset, which contains the network dataset, can participate as network sources.

System junctions

A junction must exist at each end of an edge in a network dataset. So if you don't create a junction source feature at the end of an edge, a system junction will be created automatically when the network dataset is built.

System junctions are stored as points in a source feature class, which is automatically generated during the first build operation. The source feature class is named [network name]_Junctions, where [network name] represents the name of the network dataset.

Add or remove network sources

Additional source feature classes can be added or removed from a network dataset. Follow the steps below to add or remove network sources.

  1. Open the Network Dataset Properties dialog box.
  2. Click Source Settings > Sources.

    The page displays all the source feature classes that currently participate in your network dataset.

  3. Click the Add/Remove Sources button in the upper right corner of the dialog box.

    The Add/Remove Sources dialog box appears.

    Add/Remove Sources dialog box

  4. Check or uncheck the feature class check boxes to add or remove them from your network dataset.

    Some of the check boxes may be unavailable. Hover over an unavailable check box to learn why it can't be added or removed from the network dataset. For example, the system junction feature class is required in the network dataset and cannot be removed.

  5. Click OK to close the Add/Remove Sources dialog box.

    Changes are reflected on the Sources tab.

  6. Note:

    If the source that is added or removed changes the connectivity, update the elevation connectivity and group connectivity settings on the respective tab.

    If the source that is added or removed affects the configuration of your network attributes, go to the respective network attribute tab and correct the evaluator settings for each affected attribute.

  7. Click OK on the Network Dataset Properties dialog box to save the changes to the network dataset.
  8. Note:

    When you change any network attributes, you must build the network dataset to reestablish the connectivity, recalculate affected attributes, and update the network elements.

    Learn more about when a rebuild is required