Setting signposts for directions

Signposts provide the type of directional information found on highway road signs, such as exit numbers, connecting roads, and major destinations that can be reached along the connecting roads. If you have signpost data, you can use it to enhance the route directions generated by Network Analyst. For example, the road sign in the graphic below informs northbound drivers that if they take exit 242, they will enter onto the eastbound side of Interstate 80, which connects to Brighton and Ainsworth.

Example of a signpost

A short route along the arrow in the graphic above was created and the directions, with and without signposts, are compared below. The third step in each case highlights the difference:

Directions without signposts
Directions without signposts
Directions with signposts
Directions with signposts

A driver that uses the second set of directions can avoid making a wrong turn by matching more of the information on the directions to the sign that is encountered on the road.

This signpost information for driving directions is specified by using a signpost feature class and signpost streets table. The signpost feature class describes the text on the road sign, and the signpost streets table identifies the street segments that are traversed when following directions given by the road sign.

Typically, the signpost and street data are purchased together from vendors and transferred into the proper feature class and table format using custom scripts. (For more information on custom scripts for signposts, search for "Import signposts" on the ArcGIS Resource Centers.) It is possible, but not recommended, to create signposts yourself using the format described in the following sections. In either case, once the data is prepared, both the feature class and table need to be specified in the Network Directions Properties dialog box for them to be valid.

NoteNote:

The Network Analyst tutorial data includes a San Francisco geodatabase that has signposts. Referencing it while you read this topic may be helpful.

Learn more about the Network Analyst tutorial

Signpost feature class

The signpost feature class is a line feature class. In the case of a geodatabase, it must reside in the same feature dataset as the network dataset. In the case of a shapefile network dataset, it must reside in the same workspace. A signpost feature class can support a maximum of 10 branches and 10 destinations. The table below describes the fields on a signpost feature class that supports two branches and three destinations.

Field

Format

Description

ObjectID

OID

Signpost ID (OID field).

Shape

Geometry

Geometry of the signpost (line geometry).

ExitName

Text

Exit number; for example, exit 242.

Branch0

Text

Name of the first street or highway at the end of a ramp; for example, I-80.

Branch0Dir

Text

Official direction of Branch0; for example, North, South, East, or West.

Branch0Lng

Text

Language of Branch0; for example, en, de, fr.

Branch1

Text

Name of the second street or highway that shares the physical road used by Branch0. If I-80 and Hwy. 30 shared the segment of road at the end of the ramp, "Hwy 30" would be entered here.

Branch1Dir

Text

Official direction of Branch1; for example, North, South, East, or West.

Branch1Lng

Text

Language of Branch1.

Toward0

Text

First destination beyond where the ramp ends; for example, Brighton.

Toward0Lng

Text

Language of Toward0; for example, en, de, fr.

Toward1

Text

Second destination beyond where the ramp ends; for example, Ainsworth.

Toward1Lng

Text

Language of Toward1.

Toward2

Text

Third destination beyond where the ramp ends; for example, another city or a point of interest.

Toward2Lng

Text

Language of Toward2.

Signpost featureclass schema

Signpost streets table

The signpost streets table should reside in the same geodatabase or shapefile workspace as the network dataset. The schema for the signpost streets table is as follows:

Field

Format

Description

ObjectID

OID

OID field

SignpostID

Long

Foreign key to ObjectID field on signposts feature class.

Sequence

Long

Sequence identifier for the maneuver segment. For TrueSequence maneuvers, this can be 1-K, where K is the maximum number of edges in a maneuver. For maneuvers with only first/last edges, it is 1 for the first edge, and 0 for the last.

EdgeFCID

Long

Feature class ID corresponding to the streets feature class in the signpost maneuver sequence.

EdgeFID

Long

Feature ID corresponding to the street feature in the signpost maneuver sequence.

EdgeFrmPos

Double

Used to determine the street feature where the signpost maneuver sequence begins.*

EdgeToPos

Double

Used to determine the street feature where the signpost maneuver sequence ends.*

Signpost streets table

*Notes regarding the EdgeFrmPos and EdgeToPos values:

For best performance, it is strongly recommended that the following fields on the signpost streets table have an attribute index:

Learn more about indexing an attribute

Signpost example

The following graphics and attribute tables illustrate how the green sign can be modeled:

Features and corresponding ObjectIDs used to model the signpost
Note that the language fields were removed from the Signpost attribute table in this graphic.

Related Topics

3/25/2015