Geometry and Attribute Data of Network: Link Impedance, Turns, and Restrictions (Especially for GATE-Geospatial 2022)

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Network analyses analyze the way ‘goods’ can be transported along these lines (telecommunication lines, road etc.) . Example: Undirected roads. Network analysis can be done in raster or in vector. Network analysis involves several aspects.

Diagram Shows Network Analysis

Link and Link Impedance

A link is a road segment defined by two end points. Links are the basic geometric feature of a network. Link impedance is the cost of traversing a link.

Travel time estimated from the length and the speed limit of a link. It can be directional: one direction time may be different than opposite. It may also vary by the time of the day and the day of the week.

In short, length is not only consideration:

  • Speed limits, traffic conditions vary
  • Travel may be directional – time may vary in one direction versus the other
  • Time of day, day of week, etc.

Topology Components

Figure Shows Topology Components

Junction and Turn Impedance

A junction refers to a street or intersection, also called a node. A turn is a transition from one street segment to another at a junction. If link has associated direction, node will be defined as a starting or ending node.

Turn impedance is the time it takes to complete a turn, which is significant in a congested street network. A turn table assigns the turn impedance value to each turn in the network.

Figure Shows the Turn Impedance Value to Each Turn in the Ne …

One-Way or Closed Streets

One-way directions must be set up relative to the digitized direction of the line (affecting the From-To or To-From edge) , and cannot detect line orientations relative to a compass or clock face direction.

Designed in attribute table:

  • FT – From the from-node to the to-node
  • TF - From the to-node to the from-node
  • N – Travel not allowed in either direction

Overpasses and Underpasses

Figure Shows Network Dataset Model

In the graphic to the right, a network dataset models the street network. The graphic highlights that one-way streets turn restrictions and overpasses/tunnels can be modeled. The analyses that are performed on the network, such as the route from stop 1 to stop 2, respect these and other network dataset properties.

Developed by: