Legitimate dangles created by line feature termini, such as cul-de-sacs, are a longstanding problem for GIS professionals who regularly work with linear feature data. When a topology is validated for the rule “Must Not Have Dangles” and all dangles are resolved or marked as an exception, the new Export Topology Errors geoprocessing tool in ArcMap10.1 allows for the ability to share the topological errors and exceptions with others. Sharing a Topology Error dataset is useful for fixing errors in the base layer among co-workers, but it does not help to track known topology exceptions. Once the fixed base layer is re-evaluated against a topology, any information known about legitimate dangles will be lost and reflagged as an error. This will necessitate the reevaluation of every dangle. For the case of CDOT, we are aware of ~60,000 known legitimate dangles across the statewide local roads layer, but a county-by-county workflow results in losing information about legitimate dangles every time a new topology is created or validated. Therefore, legitimate dangles have to be continually reevaluated - a huge waste of CDOT resources. The crux of the issue is the that topology layers are not selectable because they are only graphical representations of error locations. This presentation demonstrates a way to programmatically update a new topology with known topology exceptions using MS ACCESS. The result effectively makes topology layers selectable by location in order to incorporate known topology exceptions into a new topology and eliminates the need for repeat evaluation of legitimate dangles.

1. Beyond the Legitimate Dangle Impasse:
how to really share and maintain topology exceptions with the
Export Topology Errors geoprocessing tool
GIS in the Rockies 2013
October 9th
Presenters: Grant Garstka • Aaron Rhodes

2. Introduction
Legitimate Dangles - line feature
termini, such as cul-de-sacs
“Must Not Have Dangles”
topological rule -- helps to identify
the location of all dangles
While the rule finds dangles, a user
must determine if each dangle is an
error or legitimate dangle

3. Must Not Have Dangles
A line from one layer must touch lines from the same layer at both
endpoints.
Any endpoint where the line does not touch another line is an error.

4. Must Not Have Dangles
A line from one layer must touch lines from the same layer at both
endpoints.
Any endpoint where the line does not touch another line is an error.

5. Case Study
•
Arapahoe County contains 4,096 legitimate dangles
•
CDOT knows there are 4,096 dangles marked as exception and their location,
we do not want to have to ever revisit them.
•
Yet, if we create a new topology for this county’s layer and re-validate all 4,096
legitimate dangles will be flagged again as potential errors
•
This is the legitimate dangle impasse - a huge waste of CDOT resources.

6. Case Study
This issue is compounded at the state scale
83,000+ miles
of local roads in
the HUTF
inventory
greater than
60,000
legitimate
dangles
statewide

7. Export Topology Errors --10.1
February 7th. 2013 ArcGIS Resources
Overview
•Exports the errors from a geodatabase
topology to the target geodatabase.
•All information associated with the errors
and exceptions, such as the features
referenced by the error or exception, are
exported.
http://blogs.esri.com/esri/arcgis/2013/02/07/exporttopology-errors/
•Exported feature classes can be accessed
using any license level of ArcGIS.
•The feature classes can be used with the Select by Location dialog box or the
Select Layer By Location tool
•Can be shared with other users who do not have access to the topology itself.

8. A Perfect Solution?
“the outputs of the Export Topology
Errors tool are standard feature classes,
which enable [the user] to select the
error shapes interactively or through
a query, use those geometries for
subsequent spatial queries, and
share the errors with other users”
“For example, [the co-worker] can...
resolve a Must Not Have Dangles
line error by snapping lines
properly. After she finishes her edits, I
can reintroduce the updated feature
classes into the main geodatabase and
use my Standard or Advanced license
to rebuild the topology, check for
remaining errors, and repeat the
sharing process as needed”
This sounds like the answer to all of our
problems
-From ArcGIS Resources announcing the new tool
(February 7th, 2013)

9. The Real Problem
topology layers are not selectable and
cannot participate in spatial queries
topology errors are not actually
features, but rather graphical
representations of error locations
the Topology Exception feature class
created from the Export Topology Error
tool cannot be used to create a
selection set in the topology
Tool is geared toward resolving errors and not managing
and tracking exceptions

10. The Solution
Using MS ACCESS, we can programmatically join a
topology and Export Topology Errors feature class to
update a new topology with known topology exceptions
What you will need
-Personal Geodatabase containing
a) Linear Feature Class
b) New Topology
c) Feature Class from Export Topology
Errors
-MS ACCESS
The result effectively makes the topology layer
selectable by location

11. The Solution
Each feature contains 2 tables:
• Attribute Table (ObjectID)
• Shape_Index (IndexedObjectId)
ArcCatalog
Topology’s Shape Index Table
ACCESS Objects - Tables

12. The Solution
1) Design a Query with the following joins:
2) Make it an Update Query with the
following expression:
3) Run!

13. The Solution
The topology layer is now updated with known
topology exceptions.
T_1_PointError’s Table
When you open the layer in ArcMap again,
only valid topology errors will display!!

14. The Solution Summary
Create Personal GeoDatabase
Create, validate, and review topology
Export Topology Errors/Exceptions
Make new topology or use Co-workers topology
Open .mdb in MS ACCESS
Join based on X,Y and ObjectID/IndexedObjectID
Run Update Query on “isException”
Re-open ArcMap

15. Some Issues
•
In MS ACCESS, only change the values in
the tables - not the schema
•
Performance hit in ArcMap on the linear
feature, not the topology?
•
CDOT was moving towards File
GeoDatabases and away from Personal
GeoDatabase.

16. Questions?
Grant Garstka
Grant.Garstka@state.co.us
Aaron Rhodes
Aaron.Rhodes@state.co.us