Geometric Networks in ArcGIS

1
Geometric Networks in ArcGIS

• Sewer, water, roads, etc..

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

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

5
Analyze Network in ArcMapwhat 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
All are implemented with the Utility Network
Analyst toolbar
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)

7
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

8
Building and Using the Geometric Network

• Reference detail

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

10
Define Source and Sinks
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

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)

13
Add Weights to a network
14
Add complex edges and Define feature to be
snapped
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

16
Tracing upstream and downstream

• Upstream trace

• Downstream trace

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

18
Finding common ancestor

• Piece of upstream network common to all flags
• Which electric line is common to all house?

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

20
Finding Indeterminate Flow

• Use the Find Loops analysis

No Cycle (switch open)
Cycle (switch closed)
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
• 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

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)

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
24
Setting Edge-to-Edge Rules
This Edge
Connects to this edge
Through this junction