Erase (Coverage)

Summary

Creates a new output coverage by overlaying the polygons of the erase coverage with the features of the input coverage. Only those portions of the input coverage features falling outside the erase polygon outer boundaries are copied to the output coverage.

Learn more about how Erase works

Illustration

Erase example

Usage

• The output coverage cannot already exist.

• Annotation is erased if its lower left starting point falls within the erasing polygon.

• New nodes have their attributes set to zero.

• Input coverage polygons that are coincident with erase coverage polygons are removed.

• The erase coverage must have polygon topology.

• User-IDs for all features are the same in the output coverage as they are in the input coverage.

• For the POLY and NET options, polygon topology is rebuilt in the output coverage. Whenever possible, input polygon label points are preserved in the output. Each old polygon keeps its original label point position if it falls outside an erase coverage polygon.

• Boundaries of interior polygons in the erase coverage are not used in ERASE. Any erase coverage polygon whose internal number is greater than one is considered inside the erasing window; an internal polygon number of one is considered outside. Only those input features (or portions of them) that are outside the erasing region are stored in the output coverage.

• The outside boundaries of the erase coverage define the area of Input coverage features to be removed. Any erase coverage polygon with an internal number greater than one is considered inside the erasing window; an internal polygon number of one is considered outside.

• If the erase coverage polygon happens to fall completely within an input polygon, then no polygons are erased. An extra polygon is inserted in the output coverage, as defined by the outline polygon of the erase coverage, and given a label point with a User-ID = 0. This is for the POLY option. If the LINE option is used, then nothing extra is added. The output coverage remains identical to the input coverage.

• Route systems will be rebuilt for LINE, NET, LINK, and RAW options but ignored on the POLY option. Route systems are duplicated for arcs split into multiple pieces and eliminated for eliminated arcs. ERASE maintains all route system subclasses.

• Region subclasses in the input coverage are maintained with the POLY option. Regions in the input coverage are erased in the output coverage by the extent of the erase coverage.

• Region subclasses in the erase coverage are not inherited.

• If a node attribute table (NAT) exists before ERASE, then it remains afterward for those nodes that survive the ERASE. New nodes have their attributes set to zero.

• The output coverage tics are copied from the input coverage.

• The projection file (PRJ) is copied to the output coverage.

• The coordinate precision of the output coverage is determined by the current processing rule as set by the Precision for Derived Coverages environment setting. If the processing rule is not established, the output coverage is the same precision as the input coverage.

• When the input coverage contains linear data belonging to different planar graphs, the data will be maintained in the output coverage. For example, with coincident or colinear arcs, such as arcs representing utility cables at different levels or a road following a stream, the coincident and colinear line segments will be preserved. However, additional vertices may be inserted. In the case of intersecting arcs, such as a road passing over a stream, nodes will not be inserted at the apparent intersection.

• Learn more about how the default fuzzy tolerance is calculated

Syntax

Erase_arc (in_cover, erase_cover, out_cover, {feature_type}, {fuzzy_tolerance})

Parameter	Explanation	Data Type
in_cover	The coverage containing features to be erased.	Coverage
erase_cover	The coverage whose outer polygon defines the erasing region.	Coverage
out_cover	The coverage to be created.	Coverage
feature_type (Optional)	The set of features to be erased: POLY —Polygons are erased, and the polygon attribute table (PAT) is updated. This is the default. LINE —Arcs are erased, and the arc attribute table (AAT) is updated. POINT —Points are erased, and the point attribute table (PAT) is updated. NET —Polygons and arcs are erased, and their PAT and AAT are updated. LINK —Arcs and points are erased, and their AAT and PAT are updated. RAW —Arcs, data points, and annotation in a coverage that do not have topology (no attribute files) are erased. Route systems are maintained, but regions PAT and AAT are not saved.	String
fuzzy_tolerance (Optional)	The minimum distance between coordinates in the output coverage. By default, the minimum fuzzy tolerance value from the input coverage and erase coverage is used. Learn more about how the default fuzzy tolerance is calculated	Double

Code Sample

Erase example (stand-alone script)

The following stand-alone script demonstrates how to erase an area from a coverage.

# Name: Erase_Example.py
# Description: Creates an empty area inside a polygon coverage.
# Requirements: ArcInfo Workstation

# Import system modules
import arcpy
from arcpy import env

# Set environment settings
env.workspace = "C:/data"

# Set local variables
inCover = "tongass1"
eraseCover = "tong_azone"
outCover = "C:/output/tong_nozone"
featureType = "POLY"

# Execute Erase
arcpy.Erase_arc(inCover, eraseCover, outCover, featureType, "")

Environments

Current Workspace, Level Of Comparison Between Projection Files, Precision For New Coverages, Precision For Derived Coverages, Scratch Workspace

Licensing Information

ArcGIS for Desktop Basic: No

ArcGIS for Desktop Standard: No

ArcGIS for Desktop Advanced: Requires ArcInfo Workstation installed