This model [PDF-7.79 MB, 2 pages] illustrates the fundamentals of the new Network Data Set described below.

The ArcGIS Network Analyst extension available for ArcGIS 9.1 includes important capabilities for modeling transportation

Network Data Sets can incorporate multiple modes of transportation.

Transportation network modeling has many requirements and functions, including the ability to support

• Multiple travel modes, such as walking, public transit systems, and driving in automobiles, for any journey
• The options and costs of transferring between modes of travel
• Travel costs and routes that vary by time of day or the changing conditions of the network
• The ability to represent complex turn restrictions and costs between any elements in a transportation network
• Modeling a hierarchy of transportation systems (e.g., primary use of freeways between destinations combined with travel along city streets and sidewalks near each destination)
• Handling very large Network Data Sets (with millions of features) and continuous updates and edits coming simultaneously from many users

ArcGIS 9.1 Network Analyst adds capabilities to support these situations. An important consideration in any approach is the ability to model the behavior directly on the features that represent persistent network elements for the purpose of assigning costs, editing connectivity, mapping, visualizing, and numerous other uses.

Sources for a Network Data Set

A Network Data Set is built from GIS data and feature sources. These sources are feature classes and tables in a geodatabase, shapefiles, or Smart Data Compression data sets.

The ability to use existing geodatabase elements, such as feature classes of points, lines, and areas, greatly simplifies the editing and management of the network information. For example, the common work flow involves directly updating the road features and attributes representing the from–to cost traveling along a particular segment. The elements of a network graph must serve data editing and management tasks, as well as support navigation algorithms and operators.

Network Data Sets also contain navigation and restriction attributes of the following four distinct types:

• Costs—Impedances that are assigned proportionally and accumulated along network elements (e.g., edges, junctions, turns)
• Descriptors—Values that describe characteristics of network elements. Examples include speed limit, number of lanes, or bridge height
• Restrictions—Values that specify which network elements can be traversed under certain conditions, such as defining one-way streets, pedestrian use only, bus use only, etc.
• Hierarchy—Categorizes network edges into primary, secondary, or local roads to optimize the speed of network analysis and normal travel patterns

The model [PDF-7.79 MB, 2 pages] illustrates the fundamentals of the new Network Data Set.