1. Geometric Networks in ArcGIS
Sewer, water, roads, etc..
2/2008
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2. Types of Networks 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. Flow direction not determined solely by network.
Available thru Network Analyst extension
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3. 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 its integrity
My guess is that each was developed by separate teams with different primary goals, with overlap occurring in the process
Note 1: If a Topology relationship class exists in a feature dataset, you cannot build a geometric network.
Note 2: ArcEditor is required for either.

4. Creating a Network in ArcCatalog
Geometric networks are created in ArcCatalog and stored as a relationship class within a geodatabase feature dataset
Right click on a feature dataset and select New/Geometric network to 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 but they must all be in the same feature dataset
However, not all line or point feature classes in the feature dataset have to participate
The features within participating feature classes
May be moved if snapping is allowed
Have one or two new attribute fields: Enabled and Ancillary 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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5. Analyze Network in ArcMap what you can do with a network
relate lines and points together so that when a move is performed in editing all points and lines move together
Establish flow direction in network using sources and sinks
down the network to a sink or down the network from 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 the AncillaryRole field in the point feature class(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 with Barrier tool in map document (e.g pipe break now)
Semi-permanent barriers applied through the Enabled field 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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6. 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 of a pipe segment)
edges
junctions
Simple
edge
Complex
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7. Type of network flow Uninitialized Determined Undetermined
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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8. Building and Using the Geometric Network
Reference detail
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9. Building the network Select a feature dataset Name your network
Select feature classes to participate
Set snapping
Tolerance distance
Feature classes to snap to
Identify complex edge feature classes
Define Sources and Sinks
Set weights
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10. Define Source and Sinks
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11. 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 before analysis with tool
Display flow arrows via Flow/Display Arrows
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12. 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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13. Add Weights to a network
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14. Add complex edges and Define feature to be snapped
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15. 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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16. Tracing upstream and downstream
Upstream trace
Downstream trace
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17. 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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18. Finding common ancestor
Piece of upstream network common to all flags
Which electric line is common to all house?
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19. 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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20. Finding Indeterminate Flow
Use the Find Loops analysis
No Cycle (switch open)
Cycle (switch closed)
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21. 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
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

22. Setting Connectivity Rules
Connectivity rules are network versions of domains
“business rules” which you apply to connections between 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 is created by right clicking the network relationship class in ArcCatalog and going to Properties/Connectivity tab
Another option is to select Geometric Network Editor instead of going to Properties. (Probably easier once concept is understood)
GISC UT-Dallas Briggs

23. Setting Edge-to-Junction rules (and junction-to-edge)
This feature class
(edge, in this case)
With these
Cardinalities
With this subtype
Connects to
this junction
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24. Setting Edge-to-Edge Rules
This Edge
Connects to
this edge
Through this
junction
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