Im looking for a way or workflow to create Thiessen Polygons from a Line file
well unless there is something unconventional in you features, perhaps converting them back to points and regenerating the triangulation would be a good first test
Feature Vertices To Points—Help | ArcGIS Desktop
This may be Plan B. But will create significant additional work. My
Line data is a road system within a watershed.
In think Dan Patterson has the key. Be sure to check the point location (optional) settings in the tool for the one that matches your need. Also, note that an Advanced license level is required to run the tool.
Some other thoughts:
If you need to clean up your line data first, consider running a Integrate and then Dissolve in preparation for Feature Vertices to Points. Note that what settings you use for each of these will depend on how your data is organized.
Integrate—Data Management toolbox | ArcGIS Desktop
Dissolve—Data Management toolbox | ArcGIS Desktop
Note that if there are two or more geoprocessing tools that need to be run in sequence that they can be run together using Modelbuilder or Python.
What is ModelBuilder?—Help | ArcGIS for Desktop
A quick tour of Python—Help | ArcGIS for Desktop
Also, Geodatabase Topology can be of help in getting the linework coincident.
Designing a geodatabase topology—Help | ArcGIS for Desktop
Then of course, the final tool, once points have been derived
Create Thiessen Polygons—Help | ArcGIS Desktop
Chris Donohue, GISP
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