[GIS] Thiessen Polygon delineation within a Feature

arcgis-10.0arcpyspatial-analystvoronoi-thiessen

I am trying to create Thiessen (Voronoi) polygons, based on points within a defined shapefile extent.
The output should be inclusive to the feature. The output I receive now is the rectangular area around the selected points.

Steps I am using:
1. select points of interest (inside and outside spatial extent)
2. set primary display field to FID (aka:ObjectID)
3. Environment… > Set 'Analysis Mask' to shapefile with feature (in this case, a watershed)

Now here is where the problem starts.
I have a set of instructions for arc 9.3, but I am now operating on ArcGIS 10 (Spatial Analyst installed & activated).
Also, just to clarify, I did scour the inter-webs for some number of hours- Esri support, gis.SE, Professor Google…

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9.3.1 version:
Spatial Analyst >> Distance >> Allocation
– set 'Assign To' as point shapefile of selected data
– set cell size

10.0 methods tried:
Analysis >> Create Thiessen Polygons
— Many variations of selected features
— File locations, both inside and out of file geodatabase

I am open to any solution, using Arc 10.0 and/or python would be ideal. The first image is an example. The output does not need to be exact.

wiki: http://en.wikipedia.org/wiki/Voronoi_diagram

Best Answer

I may be missing something here, but I just tested on my machine to make sure. Use the Create Thiessen Polygons tool in Analysis Tools>Proximity>Create Thiessen Polygons. Then you specify your analysis mask by clicking on Environments>Processing Extent and select your feature class that has the watershed boundary. This is giving me the output you are looking for I believe, I am using Arcmap 10 as well. Let me know if I missed something here. See image below....

Thiessen Polys

The green is thiessens for the entire dataset, while the blue is theissens with an analysis mask (your watershed) specified.

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