ThiessenPolygons

Builds Thiessen Polygons from a feature layer

Thiessen (Voronoi) polygons define individual areas of influence around each of a set of points. Thiessen polygons are polygons whose boundaries define the area that is closest to each point relative to all other points. They are mathematically defined by the perpendicular bisectors of the lines between all points

Inputs:

A feature layer (Point, Polyline, Polygon)

Outputs:

New polygon feature class.
- If Attach attributes option is selected, the attributes of the source features are transferred to the new attribute table.

Notes :

The process goes through several steps
- Collects the points from a point layer (vertices if the source is a polyline or polygon layer)
- Clean duplicate points
- Generates Convex Hull
- Creates a TIN structure
- Generates perpendicular bisectors for each tin edge.
- Builds the Thiessen polygons
- Clips the Thiessen polygons feature class with the convex hull.
To achieve best results when creating Thiessen Polygons from a polyline layer use Generalize Polylines Wizard or Densify Polyline Wizard (before running the Thiessen Polygons procedure) in order to remove unnecessary points or add points to the long straight segments
By default the Thiessen polygons are clipped to the extents of the input features. There is an option to buffer the extents rectangle before clipping with it.
The resulting feature class can be clipped (Clip Layer Wizard ) with any polygon layer to mach the shape of this layer.
If the source is a polyline or polygon layer, only the attributes of the first feature found inside each Thiessen polygon will be transferred.
The function should work with no problems on datasets with up to 2 million points.

Examples of use:

Defining trade areas
From a set of soil sampling points to define non overlapping polygons for each soil type

Example:

Point Collection	Convex Hull	Thiessen Polygons

ToolBox implementation
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Command line syntax

ET_GPBuildThiessen <input_dataset> <out_feature class> {clip_buffered} {buffer_distance} {attach_attributes}

Parameters

Expression	Explanation
<input_dataset>	A Point, Polyline or Polygon feature class or feature layer
<out_feature class>	A String - the full name of the output feature class (A feature class with the same full name should not exist)
{clip_buffered}	A Boolean indicating whether the output will be restricted to the extent rectangle of the input features (False) or will be extended with the specified buffer distance (True)
{buffer_distance}	A Double setting the the distance with which the extent rectangle of all the input features will be buffered (in the units of the input dataset) to be used if the {clip_buffered} is True. If {clip_buffered} is False this parameter is ignored
{attach_attributes}	A Boolean indicating whether the attributes of the original features will be transferred to the resulting thiessen polygons

Scripting syntax

ET_GPBuildThiessen (input_dataset, out_feature class, clip_buffered, buffer_distance, attach_attributes)

See the explanations above:
<> - required parameter
{} - optional parameter