GRANT GARSTKA

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. Once 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 over time.

 

Once the fixed base layer is re-evaluated against a topology, any known information about legitimate dangles is lost and reflagged as an error. This necessitates the reevaluation of every dangle for every new topology.  For the case of The Colorado Department of Transportation (CDOT), we are aware of more than 60,000 known legitimate dangles across the statewide local roads layer. Therefore, legitimate dangles have to be continually reevaluated - a drain on time and resources.  The crux of the issue is the that topology layers are not selectable because they are only graphical representations of error locations.

 

While working for CDOT, I developed a process 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.