Geometric Networks in ArcGIS

8/3/2019 Geometric Networks in ArcGIS

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2/2008 GISC 6382 UT-Dallas Briggs 1

Geometric Networks in ArcGIS

Sewer, water, roads, etc..


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GISC 6382 UT-Dallas Briggs 2

Networks are of two types Directed flow (geometric networks) utility networks such as sewer and water systems; rivers and streams

Elements on the network have no choice in travel decision. Flow

direction is determined by the network characteristics alone.

Referred to as geometric or utility networks by ESRI

Available with ArcEditor level of ArcGIS

Undirected flow

Transportation networks such as streets

Elements on the network make their own travel decisions. Flowdirection not determined solely by network.

Available thruNetwork Analystextension

Types of Networks


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Geometric Networks and Network Topology

Geometric Networks can also be useful for checking network

topology provide an alternative approach to applying topology rules

checking editing on a line file for connectivity and overlaps

Linking points and lines into a topological structure

Network Topology

a procedure for ensuring the integrity of data applying topology rules for points and lines feature classes

examined in av9edit_topo.doc

Geometric (Utility) Network a procedure for modeling flows thru a network

However, can also be helpful in editing network data and ensuing itsintegrity

My guess is that each was developed by separate teams withdifferent primary goals, with overlap occurring in the process

Note 1: If a Topology relationship class exists in a feature dataset, youcannot build a geometric network.

Note 2: ArcEditor is required for either.


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Creating a Network in ArcCatalog Geometric networks are created in ArcCatalog and

stored as a relationshipclass within a geodatabase

feature dataset Right click on a feature dataset and select

New/Geometric networkto start the wizard for

creating the network

The network (a relationship class) and its junctions (a

point feature class) are listed along with the feature

classes

Multiple point and line feature classes can participate in a network butthey must all be in the same feature dataset

However, not all line or point feature classes in the feature dataset have toparticipate

The features within participating feature classes

May be moved if snapping is allowed

Have one or two new attribute fields:EnabledandAncillary Role (if Source/Sink)

A feature class can only participate in one network

If desired, you can create a network with empty feature classes, and

populate by editing in ArcMap, or loading data


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Analyze Network in ArcMapwhat you can do with a network

relate lines and points together so that when a move is performed in editing allpoints and lines move together

Establish flow direction in network using sources and sinks

downthe networkto a sinkor down the networkfrom a source

Intended for tracing paths through network

Also useful to find errors in edited files (lines not snapped together, etc..)

Sources and sinks are identified in theAncillaryRole field in the point featureclass(es). A junction is either: source, sink, none, Usually have only sources or sinks

Restrict flow via barriers, and observe effect on trace(pipe clog, pipe break, etc..)

Temporary barriers applied to junction or edge withBarriertool in map document

(e.g pipe break now) Semi-permanent barriers applied through theEnabledfield in point or line feature

classes in database (e.g pipe segment under construction)

Perform network analyses (e.g. find common ancestor, find connected segments)

Junction or edge Flags are the starting point for these various trace operations

sink

source

All are implemented with the Utility Network Analyst toolbar


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Key Concepts Networks are made up of:

Edges (derived from Line feature classes) These have distance and direction

Junctions (derived from Point feature classes)

All edges end at a junction

Junctions may be end point of a line or intersections between lines

If a point from a point feature class is not available to serve as a junction, a

point, called an orphan junction, is created in the junction feature class

Edges and Junctions may be simple or complex Simple edges/junctions consist of a single feature

Complex edges allows edges to connect without separate segments

Complex junctions represent multiple features

A pump station complex junction may itself consist of multiple water lines(edges) and valves (junctions)

Weights may be associated with both edges and junctions They represent the cost of traveling over that feature

They are calculated based upon an attribute of the feature (e.g. length ofa pipe segment)

edges

junctions

Simple

edgeComplex

edge


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Type of network flow

Uninitialized Flow has not yet been set for this part of the network

Determined

Flow has been set for this part of the network

Undetermined Flow cannot be determined for this part of the network

given the sources and sinks that are established

Acts the same as uninitialized flow

Same symbol used as default,but can be changed via options


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Building and Using the

Geometric Network

Reference detail


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Building the network

Select a feature dataset Name your network

Select feature classes toparticipate

Set snapping

Tolerance distance

Feature classes to snap to

Identify complex edgefeature classes

Define Sources and Sinks

Set weights


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Define Source and Sinks


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Establishing flow with sources and sinks

Flow goes from source to sinks

AncillaryRole field of junctions

A domain defines the available values

None

Source Sink

Recalculate flow after editing and beforeanalysis with tool

Display flow arrows via Flow/Display Arrows


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Network Weights

Cost to traverse an edge or junction

Based on numeric field values Lower numbers = lower resistance

Can be bidirectional (two way) by using two fields

Negative values are barriers block flow down that segment

Define when the network is created Name the weight

Apply it to a field in one or more feature classes(process similar to using a domain: define then apply)


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Add Weights to a network


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Add complex edges and

Define feature to be snapped


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Network Analysis Network Traces

Tracing upstream and downstream

Finding path

Finding common ancestor

Find connected Flags are use to define locations for tracing: 3 step process

Place the flags

Choose a trace task

Solve the trace


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Tracing upstream and

downstream Upstream trace

Downstream trace


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Finding Path

Find the best path between two flags

Upstream, downstream, connected

From first flag to second flag Flags are placed on any feature


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Finding common ancestor

Piece of upstream network common to all

flags

Which electric line is common to all house?


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Finding connected features

Finding features connected to a flag

Commonly used for isolating features

Disable layer(s) (e.g. Valves) Set Trace to Ends Property

Place a flag on the feature you want to isolate

Trace back to the disable layer


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Finding Indeterminate Flow

Use the Find Loops analysis

No Cycle (switch open) Cycle (switch closed)


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Connectivity Rules for Networks

similar to domains for geodatabases

Domains control the values that variables can assume Can apply at subtype level and also set default values

Connectivity rules allow you to control:

which edges may connect together

what junctions (points) must be used to connect these edges Can apply at subtype level and also set default values

Two types

Edge to junction rules

Edge to edge rules

Cardinality

The number of features that can connect

Number of edges a junction can connect to

Number of junctions an edge can connect


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Setting Connectivity Rules

Connectivity rules are network versions of

domains business rules which you apply to connectionsbetween features

By default, all features can connect Setting one rule means you have to set rules for

everything you want to connect This can be a lot of work!

Connectivity rules are set after the network iscreated by right clicking the network relationship

class in ArcCatalog and going toProperties/Connectivity tab Another option is to select Geometric Network Editor

instead of going to Properties. (Probably easier onceconcept is understood)


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Setting Edge-to-Junction rules(and junction-to-edge)

With this subtype

Connects to

this junction

With these

Cardinalities

This feature class(edge, in this case)


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Setting Edge-to-Edge Rules

This Edge

Connects to

this edge

Through this

junction

Geometric Networks in ArcGIS

Documents

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