copyright © 2006 by maribeth h. price 14-1 chapter 14 analyzing networks

Copyright © 2006 by Maribeth H. Price

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Chapter 14

Analyzing Networks


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Outline

• Learning the function and terminology of simple networks

• Understanding different types of networks

• Performing tracing analysis on networks

• Understanding how networks are constructed


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Geometric networks

• Built inside a feature dataset

• May have many participating feature classes

• Requires ArcEditor or ArcInfo to build


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Network components

• Composed of edges and junctions

edges

junctions


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Network structure

Geometric network is composed of feature classes

Logical network consists of tables describing network relationships


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Types of networks

Transportation NetworksMaterial moves as it wills

Utility NetworksMaterial flow dictated by network geometry and sources/sinks


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Network problems

• Transportation– What is the best path to

travel to sixteen delivery locations?

– What is the likely service area of a fire station based on travel time?

– What is the shortest path from point A to point B?

– What is the shortest path which avoids narrow streets?

• Utility networks– If a valve fails, which

customers will be affected?

– If I have to close this pipe for repairs, can I reroute water through another path to minimize service disruption?

– How will contamination at one location propagate through the network?

– Which sewer lines serve only residential customers?


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Network tracing

• Tracing solvers used to find solutions to network problems


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Flags and barriers

• Flags indicate points of interest (start, end, stops)

• Barriers stop flow through a feature

• Types should match when solving a problem

Junction flag

Junction barrier

Edge barrier

Edge flag


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Network Utility Analyst toolbar

Establish flow Solve


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Finding paths

• Place flags and barriers

• Solve

Path with fewest edges Path with construction

Default cost is number of edges traversed


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Finding shortest paths

• Use weights to override default cost

Find shortest path with distance weight

Shortest path with three stops Visited in order that

flags are placed


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Setting weights

• Analysis options

• Set for junctions or edges

• Edge weights have direction

• Usually need both directions

Possible weights: Distance, travel time, wait at stop lights, voltage or pressure drops, etc.


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Viewing flow directions

• Flow must be established for utility networks

• Flow direction symbols can be viewed and changed

• Set view scale to hide arrows at smaller scales


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Finding connected

• Find features connected to or disconnected from the flagged feature

Water lines supplied by an intake gallery


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Finding loops

• Used to find places with indeterminate flow

• Primarily used for utility networks

Flag

FlowLoop


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Directional tracing

• Find Upstream– Trace the flow from a

feature to its source

• Trace Downstream– Find the area

disrupted by a line break


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Tracing with accumulation

• Uses default cost (edges) or set weights

• Returns total cost associated with found trace


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Find Common Ancestors

• Finds common source for a set of flags

• Use to locate possible line break from a set of service calls

Probable break


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Advanced analysis

• Avoid certain features when tracing

• Trace only on unselected features to avoid certain streets


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Advanced analysis

• Return selection

• Use statistics to find length of connected water lines


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Network analysis options

• Tracing on selected or unselected features

• Inclusion of features with indeterminate flow

• Flag/barrier snapping

General options


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Results options

• Return result as drawing or as a selection

• All features or those stopping trace

• Return edges, junctions or both


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Weight filters

• Use to exclude certain weights from analysis– Screen out short

stop sign waits from longer traffice light waits


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Building networks

1 2 3 1

Simple edges—Edges may have junctions only on their endpoints

Complex edges—Edges may have junctions between their endpoints

Useful for query and management, such as a water main with many laterals


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How to build a network

• Ensure network features are topologically valid and inside a feature dataset

• Create new network for the feature dataset– Specify network layer– Simple or complex edges– Assign weights

Requires an ArcEditor or ArcInfo license.

To build a road network using your textbook data, see “Building a simple network” in the Skills Reference section.


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Tools for managing networks

• Domains and subtypes– Used to establish network attribute codes

• Pipes can only be 3-in, 6-in, or 12-in• Default sizes and flow rates for different types

• Connectivity rules– Define which features can connect to each

other and how• T-valve must connect to three pipes• 6-in line must connect to 3-in line through a

coupler

copyright © 2006 by maribeth h. price 14-1 chapter 14 analyzing networks

Documents

feature classeslogical

best path

network geometry

network relationshipscopyright

network problemscopyright

default costfind shortest

distance weightshortest

feature datasetmay