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GenerateOptimalCoordinateSystem

Summary

The GenerateOptimalCoordinateSystem object generates a SpatialReference object with a custom projected coordinate system optimal for the specified extent and intended purpose of the map or analysis.

Since there is no way to project a curved surface onto a flat surface without distortion, various map projections exist that compromise between preserving angle, area, distance, or direction. The intended purpose and extent of a map can help determine which of these properties to preserve. For example, a conformal projection may be best for a navigational map to preserve bearing, or a projection preserving area may be required to visualize or measure the relative size of features.

Syntax

GenerateOptimalCoordinateSystem(extent, property, {custom_name})

Parameter Explanation Data Type

extent

The extent of interest. The Extent object must have a spatial reference in a geographic coordinate system such as WGS84.

Extent

property

Specifies the property that will be used to represent the purpose of the projection.

  • EQUAL_AREA—The relative area of regions everywhere on earth will be preserved. Shape and distances will be distorted.

  • CONFORMAL—Angles in small areas will be preserved, so shapes, for the most part, will be preserved. Size and distances will be distorted.

  • EQUIDISTANT_ONE_POINT—Distance will be preserved when measured through the center of the projection. Area, shape, and other distances will be distorted.

  • EQUIDISTANT_MERIDIANS—Distance will be preserved when measured along meridians. Area, shape, and other distances will be distorted.

  • COMPROMISE_WORLD—Area, shape, and distance will not be specifically preserved, but a balance between these geometric properties will be created. Compromise projections are only suggested for very large areas.

Not all properties are supported for all extents of interest. The CONFORMAL and EQUIDISTANT_MERIDIANS properties are only supported for large-scale extents, and the COMPROMISE_WORLD property is only supported for full-world extents. The EQUAL_AREA and EQUIDISTANT_ONE_POINT properties are supported for all extents

String

custom_name

The name of the custom projected coordinate system. If no value is provided, the name will be Custom_Projection.

String

Return value

Data Type Explanation

SpatialReference

A SpatialReference object with the custom projected coordinate system that is optimal for the specified extent and intended purpose.

Code sample

GenerateOptimalCoordinateSystem example 1

Create a custom projected coordinate system that optimizes preserving area over a feature class's extent, and project the feature class to the custom projected coordinate system.

import arcpy

# Input features in Projected Coordinate System
infc = r"C:\Projected.gdb\Colorado_Counties"

# Get extent of features
desc = arcpy.Describe(infc)
extent = desc.extent

# Project the extent to Geographic Coordinate System WGS84
gcs_sr = arcpy.SpatialReference(4326)
prj_extent = extent.projectAs(gcs_sr)

# Create custom projected coordinate system
custom_sr = arcpy.GenerateOptimalCoordinateSystem(prj_extent, "EQUAL_AREA",
                                                  "EQUAL_AREA_COLORADO")

# Project the input features to the custom projection
fc_prj = arcpy.management.Project(infc, "TestPoly_Projected", custom_sr)
GenerateOptimalCoordinateSystem example 2

Create a simple polygon object and project it to a custom projected coordinate system with the conformal property.

import arcpy

gcs_sr = arcpy.SpatialReference(4326) # Create WGS84 spatial reference

# Create polygon
poly_info = [[20, 20], [20, 60], [60, 60], [60, 20], [20, 20]]
poly_pts = arcpy.Array([arcpy.Point(*coords) for coords in poly_info])
poly = arcpy.Polygon(poly_pts, gcs_sr)

# Create extent object from polygon
extent = poly.extent

# Create custom projected coordinate system
custom_sr = arcpy.GenerateOptimalCoordinateSystem(extent, "CONFORMAL")

# Project the polygon to the custom projection
poly_prj = poly.projectAs(custom_sr)