The network dataset layer

You visualize a network dataset in ArcMap with a network dataset layer, or simply, a network layer. Network layers store the symbology of edges; junctions; system junctions; dirty areas; and, when available, turns and traffic.

A network analysis layer can't be created without a link to a network dataset. By adding a network dataset layer to ArcMap, you are also providing a link to the network dataset and can subsequently create analysis layers using the Network Analyst toolbar.

Adding a network layer to ArcMap

To add a network layer to ArcMap, follow the steps below:

Steps:

1. Start ArcMap by clicking Start > All Programs > ArcGIS > ArcMap 10.1.
2. Click the Catalog window button on the Standard toolbar.

   The dockable Catalog window opens.

3. Using the Catalog window, navigate to the location of the network dataset and drag it into the map display or the table of contents.

   The Adding Network Layer dialog box opens.

4. Click No to only add the network dataset to the map. Optionally, click Yes to add the network dataset and all its source feature classes to the map.

   Tip:

   Typically when features are drawn in ArcMap, their location information is pulled from their geometry values. However, network datasets don't internally store the geometry of their network elements. Instead, they reference their source features and get the geometry from there. This means there is an additional step of referencing the source features after referencing the network dataset.

   You can speed up the drawing of a network by adding the source features to ArcMap, checking them on in the table of contents, then unchecking the network dataset. This way the network dataset is still available for you to create analysis layers and the geometry is directly referenced from the source features themselves. Yet, in some cases, you still need to display the network layer, for instance, to draw traffic, dirty areas, and arrows for edge restrictions.

   The network dataset is added to ArcMap as a network layer.

   The following list points out which elements a network layer renders by default when added to ArcMap initially:

   • If the network dataset doesn't have traffic data, only edges are displayed.

   • If the network dataset has traffic data, only traffic is displayed.

     • If time isn't enabled, traffic for the current time and day is shown.

     • If time is enabled, traffic for the time specified on the time slider is shown.

   Learn more about using the time slider

Network elements can be queried with the Network Identify tool on the Network Analyst toolbar and the Identify tool on the Tools toolbar. However, they cannot be selected interactively in ArcMap. Moreover, Select By Attributes, Select By Location, and Select By Graphics cannot be used to create selection sets on a network layer.

Network layer symbology

The symbology of network elements can be modified on the network layer's Layer Properties dialog box on the Symbology tab.

You can open the Layer Properties dialog box by double-clicking the name of the layer in the Table Of Contents window.

Showing and hiding network elements

You can show or hide certain types of network elements on the map by checking or unchecking them in the Show list. When a network dataset supports traffic data, only Traffic is checked by default; otherwise, only Edges is checked by default.

What are dirty areas?

Dirty areas allow you to see where edits to source features have been made since the last time the network dataset was built. Rectangles surround and highlight the portions of the network dataset that are out of date due to the edits.

When you rebuild the network, only the dirty areas are rebuilt, which can be much faster than rebuilding the entire network.

The next pair of graphics demonstrates a scenario in which dirty areas are generated:

This is an existing road network before any edits are made to source features.

Here is the same network after a road was deleted (upper right dirty area) and two roads were created (lower left dirty areas).

If properties of the network dataset are altered, the entire network dataset may be covered by a dirty area, indicating all the elements of the network need to be rebuilt.

Changing the symbology of edges, junctions, system junctions, turns, and dirty areas

You may need to modify the default symbology of items contained within a network dataset layer. The following steps show how to change the symbology for edges, junctions, system junctions, turns, and dirty areas. (Changing the symbology for traffic is described later.)

Steps:

1. Open the Layer Properties dialog box by double-clicking the network dataset layer in the ArcMap table of contents.
2. Click the Symbology tab.
3. In the Show list, click the name of the element that you want to symbolize differently.

   The element name is selected.

4. In the Symbol section to the right, click the large button, which shows an example of the current symbol on it.
5. Use the Symbol Selector dialog box that opens to define a new symbol for the element.

   Learn more about symbolizing data

6. Click OK.

   The Symbol Selector dialog box closes.

7. Click OK.

   The Layer Properties dialog box closes.

Displaying traffic

Instructions and tips for displaying traffic are covered in the Visualizing traffic topic.

Symbolizing restrictions with arrows

Arrows in a network layer are symbols that can be displayed on edges and traffic elements to mark restrictions. Although any kind of restriction can be symbolized with arrows, it's advised that you only use this dialog box to display prohibit-restrictions, such as one-way streets, bidirectional streets, and streets that prohibit traversal in both directions. To display avoid- or prefer-restrictions, such as designated roads for hazmat, you should symbolize your source features accordingly.

The steps below describe how to display arrows:

Steps:

1. Open the Layer Properties dialog box by double-clicking the network dataset layer in the ArcMap table of contents.
2. Click the Symbology tab of the Layer Properties dialog box.
3. In the Show list, click either Edges or Traffic to select it.
4. In the Symbol section to the right, click Arrows. If you are adding arrows to Traffic, click Advanced > Arrows.

   The Arrows dialog box opens.

5. Check Draw arrows on edges.
6. Choose whether you want symbols placed in the middle or at the end of edges.
7. From the Restriction Attribute drop-down list, choose the restriction you want to symbolize.
8. Choose which restrictions cause a symbol to be drawn on network edges.

   One way	Places a symbol on one-way edges. The default symbol is an arrow that points in the opposite direction of the restriction. This makes it easy to symbolize the direction of travel that is allowed on one-way streets.
   Both	Places a symbol on edges that ignore the restriction attribute—that is, it shows where travel is allowed in both directions for prohibit restrictions.
   None	Places a symbol on edges that use the restriction in both directions. For prohibit restrictions, it shows which edges are completely prohibited.

9. Click OK.

   The Arrows dialog box closes.

10. Click OK.

    The Layer Properties dialog box closes.

Applying source filters

Source filters allow you to choose a subset of network elements to draw on the map. A previous section demonstrated how to show or hide network elements based on the source feature classes they are derived from. You can further limit the drawing of network elements by writing an SQL expression. Only the features that meet the criteria specified in the expression are drawn.

The following steps demonstrate how to create a source filter:

Steps:

1. Open the Layer Properties dialog box by double-clicking the network dataset layer in the ArcMap table of contents.
2. Click the Symbology tab of the Layer Properties dialog box.
3. In the Show list, click the name of one of the following items: Edges, Traffic, Junctions, System Junctions, or Turns.
4. In the Source Filters section to the right, click the Source Filters button. If you are adding a source filter to Traffic, click Advanced > Source Filters.

   The Source Filters dialog box opens.

5. In the Show Sources list, check the source feature classes that you want to see in the map display.

You can further limit which elements from the source feature classes are drawn in the map by creating a query expression.

6. Click the name of a source feature class in the Show Sources list and enter an SQL query using the Source Query Expression pane.

   Only features that meet the criteria specified by the query are displayed in the map.

   You can repeat this step for any other source feature class in the Show Sources list.

7. Click OK.

   The Source Filters dialog box closes.

8. Click OK.

   The Layer Properties dialog box closes.

Other network layer display settings

The network layer supports scale ranges, which specify the scales at which the network layer is visible. These can be set on the General tab of the Layer Properties dialog box.

The Display tab allows you to configure symbols to scale when a reference scale is set. Additionally, you can set transparency and MapTips for the network layer there. MapTips for a network layer can be used to display either the element ID of network elements or the value of any network attribute.