Chapter 9 Network Analysis

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

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

Network components Composed of edges and junctions edges junctions

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

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

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?

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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