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.
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, and 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.

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 under 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, traffic and edge elements are checked by default; otherwise, only edges are 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 demonstrate 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

Traffic changes with the time of day and day of the week. To display traffic for a point in time, you need to use the time slider.

Steps:

1. Add a network dataset that supports traffic to ArcMap.
2. Click the Open Time Slider Window button , which is on the Tools toolbar.
3. Choose a time and date that you want to see traffic for and adjust the time slider accordingly.
   Caution:

   The time and date that you enter are specific to the time zone that is set on the Time Slider Options dialog box. This means you might enter a time and date and unknowingly be looking at a different time and date for the local time zone. For example, say the time zone on the Time Slider Options dialog box is set to eastern time and you are looking at traffic in Houston (central time). Furthermore, assume the network edges you are looking at have a time-zone attribute that is set to central time. If you move the time slider to 11:00 a.m., the edges show what traffic is like in Houston at 10:00 a.m. because the time you enter is converted to local time.

   To show the proper time, you can either offset the time slider yourself to adjust for the time difference, or you can change the time zone in the Time Slider Options dialog box to match the area you are viewing in ArcMap.

   If the network dataset doesn't have a time-zone attribute, no adjustment is necessary since the time zone is ignored.

Changing the symbology of traffic

Traffic on edges is shown as a ratio of current speed to free-flow speed and is classified into four ranges: Stop and Go, Slow, Moderate, and Free Flow. You can change the symbology and range values for any of these groups by following the steps below:

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 Traffic to select it.
4. On the right side of the dialog box, choose the time-dependent traffic attribute from the Attribute drop-down list.
5. Right-click the symbol of the category you want to change and choose Properties for Selected Symbol(s).
6. Use the Symbol Selector dialog box that opens to define a new symbol for the category.
7. Click OK.

   The Symbol Selector dialog box closes.

You can customize the range values of any of the symbols by clicking the value that you want to change in the Speed Ratio Range column and entering a new value. The value you enter becomes the upper limit of the range. The lower limit is determined by the upper limit of the range below it. The lower limit for Stop and Go is always 0, and the upper limit for Free Flow is always 1.

8. Click OK.

   The Layer Properties dialog box closes.

Tip:

If you want to show casings around traffic, add a duplicate network dataset layer below the current one in the table of contents, then change the symbols for the different speed ratio ranges to be the same color (for example, gray) and make them slightly wider than their equivalent symbols in the other network dataset layer.

Symbolizing restrictions with arrows

Arrows in a network layer are symbols that can be displayed on edges and traffic elements to mark one-way streets, bidirectional streets, and streets that are restricted in both directions. 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.

   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 restriction cases 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 allowed direction of travel.
   Both	Places a symbol on edges that aren't restricted—that is, travel is allowed in both directions.
   None	Places a symbol on edges that completely prohibit travel.

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 a 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.

   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 a SQL query using the Source Query Expression frame.

   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 will be 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.