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Writing geometries

Using insert and update cursors, scripts can create new features in a feature class or update existing ones. A script can define a feature by creating a Point object, populating its properties, and placing it in an Array. That array can then be used to set a feature's geometry using Polygon, Polyline, PointGeometry, or Multipoint geometry classes.

import arcpy
fc = "c:/data/gdb.gdb/roads"
cursor = arcpy.da.InsertCursor(fc, ["SHAPE@"])
array = arcpy.Array([arcpy.Point(5997611.48964, 2069897.7022),
                     arcpy.Point(5997577.46097, 2069905.81145)])
spatial_reference = arcpy.SpatialReference(4326)
polyline = arcpy.Polyline(array, spatial_reference)


As shown above, a single geometry part is defined by an array of points. Likewise, a multipart feature can be created from an array of arrays of points as shown below using the same cursor.

firstPart = arcpy.Array([arcpy.Point(5997624.6225, 2069868.8208),
                         arcpy.Point(5997674.94199, 2069833.81741)])
secondPart = arcpy.Array([arcpy.Point(5997616.44497, 2069862.32774),
                          arcpy.Point(5997670.57373, 2069824.67456)])

array = arcpy.Array([firstPart, secondPart])
spatial_reference = arcpy.SpatialReference(4326)
multipartFeature = arcpy.Polyline(array, spatial_reference)


When writing point features, only a single point object is used to set the geometry of a point feature. Points can also be created more easily (and efficiently) using the SHAPE@XY token (and SHAPE@M and SHAPE@Z tokens, as needed).

import arcpy

# fc is a point feature class
fc = "c:/data/gdb.gdb/stops"
cursor = arcpy.da.InsertCursor(fc, ["SHAPE@XY"])
xy = (5997594.4753, 2069901.75682)


All geometries are validated before they are written to a feature class. Issues such as incorrect ring orientation and self-intersecting polygons, among others, are corrected when the geometry is simplified before its insertion.

The following example shows how to read a set of coordinates (defined by coordsList) containing a series of linear coordinates and use them to create a new feature class.

# Create a new line feature class using a text file of coordinates.
#   Each coordinate entry is semicolon delimited in the format of ID;X;Y
import arcpy
import os

# List of coordinates (ID, X, Y)
coordsList = [[1, -61845879.0968, 45047635.4861], 
              [1, -3976119.96791, 46073695.0451],
              [1, 1154177.8272, -25134838.3511],
              [1, -62051091.0086, -26160897.9101],
              [2, 17365918.8598, 44431999.7507],
              [2, 39939229.1582, 45252847.3979],
              [2, 41170500.6291, 27194199.1591],
              [2, 17981554.5952, 27809834.8945],
              [3, 15519011.6535, 11598093.8619],
              [3, 52046731.9547, 13034577.2446],
              [3, 52867579.6019, -16105514.2317],
              [3, 17160706.948, -16515938.0553]]

# The output feature class to be created
outFC = arcpy.GetParameterAsText(0)

# Get the template feature class
template = arcpy.GetParameterAsText(1)

cur = None
    # Create the output feature class
                                        "POLYLINE", template)

    # Access spatial reference of template to define spatial
    # reference of geometries
    spatial_reference = arcpy.Describe(template).spatialReference

    # Open an insert cursor for the new feature class
    cur = arcpy.da.InsertCursor(outFC, ["SHAPE@"])

    # Create an array object needed to create features
    array = arcpy.Array()

    # Initialize a variable for keeping track of a feature's ID.
    ID = -1
    for coords in coordsList: 
        if ID == -1:
            ID = coords[0]

        # Add the point to the feature's array of points
        #   If the ID has changed, create a new feature
        if ID != coords[0]:
        array.add(arcpy.Point(coords[1], coords[2], ID=coords[0]))
        ID = coords[0]

    # Add the last feature
    polyline = arcpy.Polyline(array, spatial_reference)

except Exception as e:
    # Cleanup the cursor if necessary
    if cur:
        del cur

Multipart polygon and polyline features and polygon features with interior rings can be created by creating an array of arrays and passing that to Polygon and Polyline classes.