Simplify Polygon (Cartography)

Summary

Simplifies polygons by removing relatively extraneous vertices while preserving essential shape.

Illustration

Sample results from the simplification algorithms are shown here for comparison.

Usage

• This tool uses different simplification algorithms for different purposes. To learn more about these algorithms, see How Simplify Line and Simplify Polygon work.

  The options for the Simplification Algorithm parameter are listed below.

  • The Retain critical points (Douglas-Peucker) algorithm ("POINT_REMOVE" in Python) identifies and removes relatively redundant vertices to simplify data for display at smaller scales. It is the fastest of the simplification algorithm options in this tool. This option is often used for data compression or for coarse simplification. The angularity of the resulting polygon outlines increase significantly as the tolerance increases.
  • The Retain critical bends (Wang-Müller) algorithm ("BEND_SIMPLIFY" in Python") identifies and eliminates relatively insignificant bends to simplify data for display at smaller scales. It is typically more accurate regarding the input geometry than the Retain critical points (Douglas-Peucker) option but can take more time to process.
  • The Retain weighted effective areas (Zhou-Jones) algorithm ("WEIGHTED_AREA" in Python) identifies triangles of effective area for each vertex. The triangles are then weighted by a set of metrics to compare the flatness, skewness, and convexity of each area. The weighted areas guide the removal of their corresponding vertices to simplify the polygon outline while retaining as much character as possible.
  • The Retain effective areas (Visvalingam-Whyatt) algorithm ("EFFECTIVE_AREA" in Python) identifies triangles of effective area for each vertex to guide the removal of vertices to simplify the polygon outline while retaining as much character as possible.

• The Simplification Tolerance parameter value determines the degree of simplification. The larger the tolerance, the more coarse the resulting geometry. Smaller tolerances generate geometry that more accurately represents the input. The MinSimpTol and MaxSimpTol fields will be added to the output to store the tolerance that was used.

  • For the Retain critical points (Douglas-Peucker) algorithm, the tolerance is the maximum allowable perpendicular distance between each vertex and the newly created line.
  • For the Retain critical bends (Wang-Müller) algorithm, the tolerance is the diameter of a circle that approximates a significant bend.
  • For the Retain weighted effective areas (Zhou-Jones) algorithm, the square of the tolerance is the area of a significant triangle defined by three adjacent vertices. The further a triangle deviates from equilateral, the higher weight it is given, and the less likely it is to be removed.
  • For the Retain effective areas (Visvalingam-Whyatt) algorithm, the square of the tolerance is the area of a significant triangle defined by three adjacent vertices.

• Polygons that are smaller than the Minimum Area parameter value will be removed from the output feature class. For a group of adjacent polygons that share common edges, the minimum area applies to the total area of the group. Use the Keep collapsed points parameter to retain a record of removed polygons as point features.

• Multipart polygons are simplified as individual parts.

• Use the Keep collapsed points parameter to create an output point feature class to store points that represent any polygons that are removed because they are smaller than the minimum area. The point output is derived; it will use the same name and location as the Output Feature Class parameter value but with a _Pnt suffix. The output polygon feature class contains all the fields from the input feature class. The output point feature class will not contain these fields.

• Topological errors such as self-intersections and overlaps between features may be created when simplifying geometry. The Handling Topological Errors parameter has three options for determining what happens in these cases:

  • Do not check for topological errors—Topological errors will not be identified. Processing will be faster. Use this option when you have confidence in the topological accuracy of the data.
  • Flag topological errors—Topological errors will be identified and flagged. The output feature class will include the InPoly_FID and SimPgnFlag fields. The InPoly_FID field will contain the input feature IDs. The SimPgnFlag field will contain a value of 1 if a topological error is present or a value of 0 (zero) if no error is present.
  • Resolve topological errors—Topological errors will not be created in the output, and errors that exist in the input will have vertices inserted at the points of intersection. Existing topological relationships between features such as shared edges will be retained. Processing time will be longer. The output feature class will include the InPoly_FID and SimPgnFlag fields. The InPoly_FID field will contain the input feature ID. The SimPgnFlag field values are as follows:
    • 0 = No topological errors are present.
    • 1 = A topological error is present in the input.
    • 2 = The feature has been split by a partition and the parts are now smaller than the minimum area after simplification. The flag may appear on only one part of the split feature. These features will be retained in the output feature class. This only occurs when the Cartographic Partitions environment setting is used.

  Legacy:

  In the course of topology resolution, previous versions of the tool modified tolerance on a per-feature basis and stored those values in the MinSimpTol and MaxSimpTol fields. In the current implementation, the values in these fields will be the same and equal to the value specified for the Simplification Tolerance parameter. Be sure to modify existing models or scripts that rely on these fields.

• Use the Input Barrier Layers parameter to identify features that must not be crossed by simplified polygons. Barrier features can be points, lines, or polygons.

• Domains and subtypes will be copied to the output even if the Transfer Geodatabase Field Properties environment is not checked.

• Processing large datasets may exceed memory limitations. In this case, consider processing input data by partition by identifying a relevant polygon feature class in the Cartographic Partitions environment setting. Portions of the data defined by partition boundaries will be processed sequentially. The resulting output feature class will be seamless and consistent at partition edges. See Generalizing large datasets using partitions for more information.

  Caution:

  The Cartographic Partitions environment setting is ignored when the Handling Topological Errors parameter is set to Do not check for topological errors or Flag topological errors.

Parameters

Dialog

Label	Explanation	Data Type
Input Features	The input polygon features that will be simplified.	Feature Layer
Output Feature Class	The simplified output polygon feature class. It will contain all the fields from the input feature class. The output polygon feature class is topologically correct. The tool does not introduce topology errors, but topological errors in the input data will be flagged in the output polygon feature class. The output feature class will include the InPoly_FID and SimPgnFlag fields to contain the input feature IDs and the input topological errors or discrepancies, respectively. The SimPgnFlag attribute values are as follows: SimPgnFlag = 0 indicates that no errors are present. SimPgnFlag = 1 indicates a topological error is present. SimPgnFlag = 2 indicates features that have been split by a partition and are now smaller than the minimum area after simplification. The flag may appear on only one part of the split feature. These features will be retained in the output feature class. This situation occurs only when the Cartographic Partitions environment setting is used.	Feature Class
Simplification Algorithm	Specifies the polygon simplification algorithm that will be used. Retain critical points (Douglas-Peucker)—Critical points that preserve the essential shape of a polygon outline will be retained, and all other points will be removed (Douglas-Peucker). This is the default. Retain critical bends (Wang-Müller)—Critical bends will be retained, and extraneous bends will be removed from a line (Wang-Müller). Retain weighted effective areas (Zhou-Jones)—Vertices that form triangles of effective area that have been weighted by triangle shape will be retained (Zhou-Jones). Retain effective areas (Visvalingam-Whyatt)—Vertices that form triangles of effective area will be retained (Visvalingam-Whyatt).	String
Simplification Tolerance	The degree of simplification that will be used. You can choose a preferred unit; otherwise, the units of the input will be used. The MinSimpTol and MaxSimpTol fields will be added to the output to store the tolerance that was used when processing occurred. For the Retain critical points (Douglas-Peucker) algorithm, the tolerance is the maximum allowable perpendicular distance between each vertex and the newly created line. For the Retain critical bends (Wang-Müller) algorithm, the tolerance is the diameter of a circle that approximates a significant bend. For the Retain weighted effective areas (Zhou-Jones) algorithm, the square of the tolerance is the area of a significant triangle defined by three adjacent vertices. The further a triangle deviates from equilateral, the higher weight it is given, and the less likely it is to be removed. For the Retain effective areas (Visvalingam-Whyatt) algorithm, the square of the tolerance is the area of a significant triangle defined by three adjacent vertices.	Linear Unit
Minimum Area (Optional)	The minimum area for a polygon to be retained. The default value is zero, that is, to keep all polygons. You can choose a preferred unit for the specified value; otherwise, the units of the input will be used.	Areal Unit
Handling Topological Errors (Optional)	Specifies how topological errors will be handled. Topological errors may be introduced in the simplification process and can include lines crossing or overlapping lines. Do not check for topological errors—Topological errors will not be identified. This is the default. Flag topological errors—Topological errors will be flagged. Resolve topological errors—Topological errors will be resolved.	String
Keep collapsed points (Optional)	Specifies whether an output point feature class will be created to store the centers of polygons that are removed because they are smaller than the Minimum Area parameter value. The point output is derived; it will use the same name and location as the Output Feature Class parameter value but with a _Pnt suffix. Checked—A derived output point feature class will be created to store the centers of polygons that are removed because they are smaller than the minimum area. This is the default. Unchecked—A derived output point feature class will not be created.	Boolean
Input Barrier Layers (Optional)	The inputs containing features to act as barriers for simplification. Resulting simplified polygons will not touch or cross barrier features. For example, when simplifying forested areas, the resulting simplified forest polygons will not cross road features defined as barriers.	Feature Layer

Derived Output

Label	Explanation	Data Type
Polygons Collapsed To Zero Area	When the Keep collapsed points parameter is checked, an output point feature class is created to store points that represent polygons that are removed because they are smaller than the minimum area.	Feature Class

Python

arcpy.cartography.SimplifyPolygon(in_features, out_feature_class, algorithm, tolerance, {minimum_area}, {error_option}, {collapsed_point_option}, {in_barriers})

Name	Explanation	Data Type
in_features	The input polygon features that will be simplified.	Feature Layer
out_feature_class	The simplified output polygon feature class. It will contain all the fields from the input feature class. The output polygon feature class is topologically correct. The tool does not introduce topology errors, but topological errors in the input data will be flagged in the output polygon feature class. The output feature class will include the InPoly_FID and SimPgnFlag fields to contain the input feature IDs and the input topological errors or discrepancies, respectively. The SimPgnFlag attribute values are as follows: SimPgnFlag = 0 indicates that no errors are present. SimPgnFlag = 1 indicates a topological error is present. SimPgnFlag = 2 indicates features that have been split by a partition and are now smaller than the minimum area after simplification. The flag may appear on only one part of the split feature. These features will be retained in the output feature class. This situation occurs only when the Cartographic Partitions environment setting is used.	Feature Class
algorithm	Specifies the polygon simplification algorithm that will be used. POINT_REMOVE—Critical points that preserve the essential shape of a polygon outline will be retained, and all other points will be removed (Douglas-Peucker). This is the default. BEND_SIMPLIFY—Critical bends will be retained, and extraneous bends will be removed from a line (Wang-Müller). WEIGHTED_AREA—Vertices that form triangles of effective area that have been weighted by triangle shape will be retained (Zhou-Jones). EFFECTIVE_AREA—Vertices that form triangles of effective area will be retained (Visvalingam-Whyatt).	String
tolerance	The degree of simplification that will be used. You can choose a preferred unit; otherwise, the units of the input will be used. The MinSimpTol and MaxSimpTol fields will be added to the output to store the tolerance that was used when processing occurred. For the POINT_REMOVE algorithm, the tolerance is the maximum allowable perpendicular distance between each vertex and the newly created line. For the BEND_SIMPLIFY algorithm, the tolerance is the diameter of a circle that approximates a significant bend. For the WEIGHTED_AREA algorithm, the square of the tolerance is the area of a significant triangle defined by three adjacent vertices. The further a triangle deviates from equilateral, the higher weight it is given, and the less likely it is to be removed. For the EFFECTIVE_AREA algorithm, the square of the tolerance is the area of a significant triangle defined by three adjacent vertices.	Linear Unit
minimum_area (Optional)	The minimum area for a polygon to be retained. The default value is zero, that is, to keep all polygons. You can choose a preferred unit for the specified value; otherwise, the units of the input will be used.	Areal Unit
error_option (Optional)	Specifies how topological errors will be handled. Topological errors may be introduced in the simplification process and can include lines crossing or overlapping lines. NO_CHECK—Topological errors will not be identified. This is the default. FLAG_ERRORS—Topological errors will be flagged. RESOLVE_ERRORS—Topological errors will be resolved.	String
collapsed_point_option (Optional)	Specifies whether an output point feature class will be created to store the centers of polygons that are removed because they are smaller than the minimum_area parameter value. The point output is derived; it will use the same name and location as the out_feature_class parameter value but with a _Pnt suffix. KEEP_COLLAPSED_POINTS—A derived output point feature class will be created to store the centers of polygons that are removed because they are smaller than the minimum area. This is the default. NO_KEEP—A derived output point feature class will not be created.	Boolean
in_barriers [in_barriers,...] (Optional)	The inputs containing features to act as barriers for simplification. Resulting simplified polygons will not touch or cross barrier features. For example, when simplifying forested areas, the resulting simplified forest polygons will not cross road features defined as barriers.	Feature Layer

Derived Output

Name	Explanation	Data Type
out_point_feature_class	When the collapsed_point_option parameter is KEEP_COLLAPSED_ POINTS, an output point feature class is created to store points that represent polygons that are removed because they are smaller than the minimum area.	Feature Class

Code sample

SimplifyPolygon example 1 (Python window)

The following Python window script demonstrates how to use the SimplifyPolygon function in immediate mode.

import arcpy
arcpy.env.workspace = "C:/data"
arcpy.cartography.SimplifyPolygon(
    "soils.shp", 
    "C:/output/output.gdb/simplified_soils", 
    "POINT_REMOVE", 
    100)

SimplifyPolygon example 2 (stand-alone script)

The following stand-alone script demonstrates how to use the SimplifyPolygon function.

# Name: SimplifyPolygon_Example2.py
# Description: Eliminate small islands before simplifying and smoothing lake 
#              boundaries.

# Import system modules
import arcpy
 
# Set environment settings
arcpy.env.workspace = "C:/data/Portland.gdb/Hydrography"
 
# Set local variables
inLakeFeatures = "lakes"
eliminatedFeatures = "C:/data/PortlandOutput.gdb/lakes_eliminated"
simplifiedFeatures = "C:/data/PortlandOutput.gdb/lakes_simplified"
smoothedFeatures = "C:/data/PortlandOutput.gdb/lakes_smoothed"

# Eliminate small islands in lake polygons.
arcpy.management.EliminatePolygonPart(inLakeFeatures, eliminatedFeatures, 100, 
                                      "OR", 0, "CONTAINED_ONLY")
 
# Simplify lake polygons
arcpy.cartography.SimplifyPolygon(eliminatedFeatures, simplifiedFeatures, 
                                  "POINT_REMOVE", 50, 200, "#", 
                                  "KEEP_COLLAPSED_POINTS")

# Smooth lake polygons
arcpy.cartography.SmoothPolygon(simplifiedFeatures, smoothedFeatures, "PAEK", 100, 
                 "FLAG_ERRORS")

Environments

Cartographic Partitions, Current Workspace, Default Output Z Value, Output M Domain, Output XY Domain, Output Coordinate System, Extent, Output has M values, Output has Z values, Scratch Workspace, XY Tolerance

Licensing information

• Basic: No
• Standard: Yes
• Advanced: Yes