1. Chapter 9
Network Analysis

2. Outline What is networks? Types of networks Network analysis
Generic trace solvers
Utility trace solvers

3. What is networks? Geometric networks
Any system of interconnected linear features is a network.
Geometric networks
Built inside a feature dataset
May have many participating feature classes
Requires ArcEditor or ArcInfo to build

4. Network components
Composed of edges and junctions
edges
junctions

5. Network structure Geometric network is composed of feature classes
Logical network consists of tables describing network relationships

6. Types of networks Transportation Networks Material moves as it choose
Utility Networks
Material flow dictated by network geometry and sources/sinks

7. Network problems Utility networks Transportation
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?
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?

8. Network analysis Network tracing
Tracing solvers used to find solutions to network problems

9. 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
Edge flag
Junction barrier
Edge barrier

10. Generic trace solvers Finding paths Place flags and barriers Solve
Path with fewest edges
Path with construction

11. Finding paths
Default cost is number of edges traversed
The path with the fewest edges is the default, but it is not always the shortest path.
To find the shortest path, you must use weights.
Path with fewest edges

12. Finding shortest paths
Use weights to override default cost
Find shortest path with distance weight
Path with fewest edges

13. What are weights?
Weights are attributes associated with features that describe the cost of traversing the feature
Edge costs might represent
The distance of the edge
The travel time along the edge
The slope along a hiking trail
Junction costs might represent
The wait time at a traffic light or stop sign
Pressure drop at a pipe junction

14. Creating weights Weights are created when the network is established.
If the weights do not already exist in the network, you cannot use them.

15. Multiple stops You can find shortest paths with multiple stops.
The user specifies the order of the stops and the solver finds the best path.
Finding the best order of a set of stops is a famous and more difficult problem—the traveling salesman problem.
Shortest path with three stops
Visited in order that flags are placed

16. Finding connected
Find features connected to or disconnected from the flagged feature
Water lines supplied by an intake gallery

17. Utility trace solvers Finding loops
Used to find places with indeterminate flow
Primarily used for utility networks

18. Directional tracing Find Upstream Trace Downstream
Trace the flow from a feature to its source
Trace Downstream
Find the area disrupted by a line break

19. Tracing with accumulation
Uses default cost (edges) or set weights
Returns total cost associated with found trace

20. 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

21. Advanced analysis Avoid certain features when tracing
Trace only on unselected features to avoid certain streets

22. Advanced analysis Return selection
Use statistics to find length of connected water lines

23. References Price, M. (2013). Mastering ArcGIS (6th ed.). McGraw-Hill
Price, M. (2013). Mastering ArcGIS (6th ed.). McGraw-Hill. Mastering ArcGIS, 6/e Instructor Edition Chapter 9: PowerPoint Notes and Figures