Network and Dynamic Segmentation

Chapter 16

Introduction

A network consists of connected linear features.Dynamic segmentation is a data model that is built upon lines of a network and allows the use of real-world coordinates with linear measures such as mileposts.Both models must have the appropriate attributes for real-world applications.

Introduction

ARC/INFO can work with both network and dynamic segmentationArcView with Network Analyst can do network model

Network

A network is a line coverage, which is topology-based and has the appropriate attributes for the flow of objects such as traffic.Examples: links, turns, one-way streets, overpass, underpass; impedance

Link Impedance

Link impedance: measure of the cost of traversing a link; cost rather than length, such as travel time (30 vs 10 mph).Directional differences (to-from node)Time of dayDay of week

Turn Impedance

Transition from one arc to anotherTime to make the turnTurn table because of changing conditions; node number, arc numbers, turn impedanceStraight, left, right, possibly UUsually directionalNegative impedance for prohibited activity

Putting Together a Street Network

Preliminary coverage from TIGER, convert to real world coordinates.Edit and update: attributes, new/changed streets, pseudo nodes for attributes change.Add impedance values.Consistent one-way streets and directionsCreate turn table

Network Applications

Shortest Path Analysis path with minimum cumulative impedance

between nodes in-vehicle Route Guidance System (RGS)

Traveling salesman problem more complex must visit each one time must return to original stop

Many algorighms

Network Applications

Shortest Path AnalysisARC/INFO has PATH and TOURArcView Network Analyst has “Find Best Route”Both create a route and option of providing directions

Network Applications

Closest Facility Computes shortest paths from the

selected location to all candidate facilities and then chooses the closest facility

Network Applications

Allocation Study of spatial distribution of resources

through a network Often refer to public facilities service

zones Efficiency is response time

Location-Allocation Minimize use of resources using facilities

and at the same time meeting objectives

Network Applications

Maximum covering model maximizes the demand covered within a

specified time or distance.

Urban Transportation Planning Model typically uses four-step process of trip

generation, trip distribution, modal choice, and trip assignment

complex, must have arc-node topology

Dynamic Segmentation

Built upon arcs of a networkBasic elements of routes, sections, and eventsRoute is a collection of sections and resides in a line coverage as a subclassSection refers directly to arcs in the line coverage and provides measures to route systemEvents are occurrences related to the route system

Creating Routes

On new arcsOn existing ArcsDifferent types of routes simple (one direction without loop or

branch) combined (route is joined by another route) split route (route subdivides into two routes) looping route (route intersects itself)

Event Tables

Events are attribute data measured on a linear reference system point events, such as accidents and

stop signs continuous events, such as speed

limits (always present) linear events, such as pavement

conditions (off and on situations)

Applications of Dynamic Segmentation

Display, query, and analysis of routes, measures, and events.Analysis of accidentsChanges