Troubleshooting network analyses
Release 9.3 Last modified March 2, 2010	Print all topics in : "Performing network analysis"

In ArcGIS Network Analyst, you may encounter certain error messages or unexpected behaviors. Ensure that you have turned on Errors and Warnings in the Network Analyst Options dialog box to understand the solution operation. You can open the Network Analyst Options dialog box by clicking the Network Analyst menu on the Network Analyst toolbar, then clicking the Options command.



You can refer to the general behavior section below to understand what kinds of errors are reported by ArcGIS Network Analyst and why they occur.
Additionally, the solver-specific behavior section below discusses how Network Analyst solvers behave in different scenarios—for example, what happens during route analysis when the origin is not located on the network.

General Behavior

There are five kinds of errors reported by Network Analyst, as discussed in the table below. The order in which these errors are discovered are as follows:

1. Errors in definition
   
2. Invalid locations
   
3. Cardinality issues
   
4. Reachability issues
   
5. User aborted
   

Type of issue	Description	Example	Output
Errors in definition	The analysis problem is incorrectly defined.	During route analysis, the attribute used as impedance is not found, as it is incorrectly named, for example, "Unable to find attribute Times." During route analysis, hierarchy settings are invalid; for example, "Invalid max value 2 for hierarchy level 2. Has to be greater than hierarchy value 3 for hierarchy level 1."	An error message is generated. No solution is found.
Invalid locations	Some or all of the network locations are not located on the network. In such cases, two alternatives exist: Invalid locations are ignored. Invalid locations are not ignored.	During route analysis, some of the stops are not located on the network. A stop is located on an edge that is restricted in both directions. A stop is located on a edge that is blocked at both ends with barriers. A located stop has incorrect time window attributes.	If invalid locations are ignored, a partial solution is found using the located network locations. Additionally, a warning message is generated about the unfound network locations that were ignored. If invalid locations are not ignored, no solution is found and an error message is generated.
Cardinality issues	The number of valid locations is less than the minimum number of locations required for the analysis.	During route analysis, there is only one valid network location.	An error message is generated. No solution is found.
Reachability issues	Some of the network locations cannot be reached.	Part of the network is not connected to or is isolated from the remaining network. Hierarchy is disconnected or incorrect. During closest facility analysis, the closest facility lies beyond the cutoff cost.	Output depends on the solver and the analysis settings. In some cases, a partial solution with a warning message is found. In other cases, no solution is found, and an error message is generated.
User Abort	The user aborts the analysis by pressing the Esc key.	During route analysis, the user presses the Esc key after clicking the Solve button and before the analysis is complete.	An Abort message is generated.

Solver-specific behavior

The following rules apply to each solver:

Route solver

• At least two stops per route are required for a solution.
  
• There can be no solution if no route is found.
  
• If invalid locations are set to be ignored, then all invalid locations are ignored (stops as well as barriers). Additionally, the sequence number of all stops is not changed (unless the Reorder Stops To Find Optimal Route option is used).
  
• If you have valid stops and one of them is unreachable, no solution is found to any stop (unless the Reorder Stops To Find Optimal Route option is used).
  
• The sequence number must be valid, that is, it must be greater than zero, cannot exceed the number of stops, and cannot be a duplicate value.
  

Route solver using the Reorder Stops To Find Optimal Route option

• If invalid locations are set to be ignored, then all invalid locations are skipped. The stops are resequenced such that the invalid locations are moved to the end of the list. If the first stop is an invalid location, the second stop becomes the first one, and the first stop is moved to the end of the list.
  
• If you have valid stops and one of them is unreachable, the stops are reordered and the unreachable stop is moved to the end of the list. A partial solution is found. This means that the route is calculated for the reachable, valid stops.
  
• If the option to Preserve First Stop (or Preserve Last Stop) is checked, then the first stop (or the last stop) must be reachable. If it is unreachable, no solution is found.
  

Closest facility solver

• At least one valid, reachable incident and one valid, reachable facility are required for a solution.
  
• If there is no valid or reachable facility for any incident, no solution is found.
  
• If there are some incidents that have no valid or reachable facility, a partial solution is found as long as at least one valid, reachable incident and one valid, reachable facility are present.
  
• If invalid locations are set to be ignored, then all invalid locations are ignored (facilities, incidents, and barriers).
  

Service area solver

• At least one valid, reachable facility is required for a solution.
  
• If there are no traversable edges for any facility, no solution is found.
  
• If there are some facilities with no traversable edges, a partial solution is found as long as there exists at least one facility with traversable edges.
  
• If invalid locations are set to be ignored, then all invalid locations are ignored (facilities and barriers).
  

OD cost matrix solver

• At least one valid, reachable origin and one valid, reachable destination are required for a solution.
  
• If there is no valid or reachable destination for any origin, no solution is found.
  
• If there are some origins with no valid or reachable destinations, a partial solution is found as long as there exists at least one valid and reachable destination for at least one valid and reachable origin.
  
• If invalid locations are set to be ignored, then all invalid locations are ignored (origins, destinations, and barriers).
  

Vehicle routing problem solver

• At least one order, depot, and route are required for a given vehicle routing problem analysis layer to be solved.
  
• The invalid network locations in Orders, Depots, and Barriers network analysis classes cannot be ignored. An error message is generated if any of these network analysis classes have invalid network locations.
  
• The attributes in the network analysis classes that act as key fields must have identical values. For example, the value for the Name attribute in the Depots network analysis class must be identical to the value for the StartDepotName and EndDepotName attributes in the Routes network analysis class. Similarly, the value for the Name attribute in the Routes network analysis class must be identical to the value for the RouteName attribute in the Breaks network analysis class.
  
Learn more about relationships between network analysis classes in a vehicle routing problem.

• If distance-based constraints such as MaxTotalDistance and CostPerUnitDistance are specified for routes, then the Distance Attribute property has to be specified for the analysis layer.
  
• If the VRP solver cannot assign all the orders to the routes without violating the given constraints, a partial solution is determined by the solver. The ViolatedConstraints attribute in the Orders and Routes network analysis classes contains information about the constraints that are violated by a particular order or the route.
  
Learn more about violated constraints for orders and routes.

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