Read geometries

Each feature in a feature class contains a set of points defining the vertices of a polygon or line, or a single coordinate defining a point feature. These points can be accessed with geometry objects (Polygon, Polyline, PointGeometry, or MultiPoint), which returns them in an array of Point objects.

Features can have multiple parts. The geometry object's partCount property returns the number of parts for a feature. The getPart method returns an array of point objects for a particular part of the geometry if an index is specified. If an index is not specified, an array containing an array of point objects for each geometry part is returned.

PointGeometry features return a single Point object instead of an array of point objects. All other feature types—polygon, polyline, and multipoint—return an array of point objects, or if the feature has multiple parts, an array containing multiple arrays of point objects.

If a polygon contains holes, it consists of a number of rings. The array of point objects returned for a polygon contains the points for the exterior ring and all inner rings. The exterior ring is always returned first, followed by inner rings, with null point objects as the separator between rings. Whenever a script is reading coordinates for polygons in a geodatabase or shapefile, it should contain logic for handling inner rings if this information is required by the script; otherwise, only the exterior ring is read.

A multipart feature is composed of more than one physical part but only references one set of attributes in the database. For example, in a layer of states, the state of Hawaii could be considered a multipart feature. Although composed of many islands, it would be recorded in the database as one feature.

A ring is a closed path that defines a two-dimensional area. A valid ring consists of a valid path, such that the from and to points of the ring have the same x,y coordinates. A clockwise ring is an exterior ring, and a counterclockwise ring defines an interior ring.

Learn more about writing geometries

Using geometry tokens

Geometry tokens can also be used as shortcuts in place of accessing full geometry objects. Additional geometry tokens can be used to access specific geometry information. Accessing the full geometry is more time-consuming. If you only need specific properties of the geometry, use tokens to provide shortcuts to access geometry properties. For instance, SHAPE@XY returns a tuple of x,y coordinates that represent the feature's centroid.

Token	Explanation
SHAPE@	Objeto de geometría para la entidad.
SHAPE@XY	Una tupla de las coordenadas x,y del centroide de la entidad.
SHAPE@TRUECENTROID	Una tupla de las coordenadas x,y del centroide de la entidad. Devuelve el mismo valor que SHAPE@XY.
SHAPE@X	Un doble de la coordenada x de la entidad.
SHAPE@Y	Un doble de la coordenada y de la entidad.
SHAPE@Z	Un doble de la coordenada z de la entidad.
SHAPE@M	Un doble del valor m de la entidad.
SHAPE@JSON	La cadena de caracteres JSON de Esri que representa la geometría.
SHAPE@WKB	Representación binaria conocida (WKB) para geometría OGC. Ofrece una representación portátil de un valor de geometría como una transmisión contigua de bytes.
SHAPE@WKT	Representación en texto conocida (WKB) para geometría OGC. Ofrece una representación portátil de un valor de geometría como cadena de caracteres.
SHAPE@AREA	Un doble del área de la entidad.
SHAPE@LENGTH	Un doble de la longitud de la entidad.

Reading point geometries

The examples below use SearchCursor to print the coordinates for all features.

Search cursor on a point feature class

import arcpy

infc = arcpy.GetParameterAsText(0)

# Enter for loop for each feature
for row in arcpy.da.SearchCursor(infc, ["SHAPE@XY"]):
    # Print x,y coordinates of each point feature
    x, y = row[0]
    print("{}, {}".format(x, y))

With the above feature class, the script returns the following information:

2.0 4.0
8.0 10.0
7.0 5.0

Reading multipoint geometries

Search cursor on a multipoint feature class

import arcpy

infc = arcpy.GetParameterAsText(0)

# Enter for loop for each feature
for row in arcpy.da.SearchCursor(infc, ["OID@", "SHAPE@"]):
    # Print the current multipoint's ID
    print("Feature {}:".format(row[0]))

    # For each point in the multipoint feature,
    #  print the x,y coordinates
    for pnt in row[1]:
        print("{}, {}".format(pnt.X, pnt.Y))

With the feature class above, the script returns the following information:

Feature 0:
3.0 8.0
4.0 4.0
6.0 6.0
Feature 1:
5.0 9.0
8.0 10.0
Feature 2:
9.0 5.0

Reading polyline or polygon geometries

Search cursor on a polygon or line feature class

import arcpy

infc = arcpy.GetParameterAsText(0)

# Enter for loop for each feature
for row in arcpy.da.SearchCursor(infc, ["OID@", "SHAPE@"]):
    # Print the current polygon or polyline's ID
    print("Feature {}:".format(row[0]))
    partnum = 0

    # Step through each part of the feature
    for part in row[1]:
        # Print the part number
        print("Part {}:".format(partnum))

        # Step through each vertex in the feature
        for pnt in part:
            if pnt:
                # Print x,y coordinates of current point
                print("{}, {}".format(pnt.X, pnt.Y))
            else:
                # If pnt is None, this represents an interior ring
                print("Interior Ring:")

        partnum += 1

With the feature class above, the script returns the information below. Feature 0 is a single-part polygon, feature 1 is a two-part polygon, and feature 2 is a single-part polygon with an interior ring.

Feature 0:
Part 0:
3.0 8.0
1.0 8.0
2.0 10.0
3.0 8.0
Feature 1:
Part 0:
5.0 3.0
3.0 3.0
3.0 5.0
5.0 3.0
Part 1:
7.0 5.0
5.0 5.0
5.0 7.0
7.0 5.0
Feature 2:
Part 0:
9.0 11.0
9.0 8.0
6.0 8.0
6.0 11.0
9.0 11.0
Interior Ring:
7.0 10.0
7.0 9.0
8.0 9.0
8.0 10.0
7.0 10.0