Define Projection (Data Management Tools)

Summary

Overwrites the coordinate system information (map projection and datum) stored with a dataset. This tool is intended for datasets that have an unknown or incorrect coordinate system defined.

Usage

All geographic datasets have a coordinate system that is used throughout ArcGIS to display, measure, and transform geographic data. If the coordinate system for a dataset is unknown or incorrect, you can use this tool to specify the correct coordinate system.
This tool only updates the existing coordinate system information; it does not modify any geometry. To transform the geometry to another coordinate system, use the Project tool.
When a dataset with a known coordinate system is input to this tool, the tool will issue a warning message but will run successfully.
All feature classes in a geodatabase feature dataset are in the same coordinate system. The coordinate system for a feature dataset should be determined when it is created.
The tool does not support the following:
- A feature class in an enterprise geodatabase
- A feature class in a feature dataset
- A feature dataset that contains a feature class
Defining a coordinate system is not supported under the following conditions:
- The input is a feature class in an enterprise geodatabase and has existing records.
  - The geometry of each record includes coordinate system metadata. Since this tool only updates the coordinate system of the feature class, the input is blocked to avoid a mismatch between the dataset's and the geometry's coordinate systems.
  - Instead of using this tool, create a feature class with the correct coordinate system, and use the Append tool to load the data to the new feature class. This projects the geometries to the coordinate system of the new feature class. Alternatively, export the features to a file geodatabase. Then run this tool to correct the coordinate system, and export the feature class back to the enterprise geodatabase.
- The input is a feature class in a feature dataset in a geodatabase. The feature dataset determines the coordinate system for all feature classes in it.
- The input is a feature dataset in a geodatabase. Don't modify the coordinate system of an existing feature dataset. This is to avoid corrupting coordinate system information of any feature class in the dataset.
The tool will update the associated .wld file of a CAD or BIM file to retain the data's geographic adjusted position.

Label	Explanation	Data type
Input Dataset or Feature Class	The dataset or feature class whose projection will be defined.	Feature Layer; Geodataset
Coordinate System	The coordinate system that will be applied to the input.	Coordinate System

Derived output

Label	Explanation	Data type
Update Input Dataset or Feature Class	The updated input geodataset.	Geodataset

arcpy.management.DefineProjection(in_dataset, coor_system)

Name Explanation Data type

Name	Explanation	Data type
in_dataset	The dataset or feature class whose projection will be defined.	Feature Layer; Geodataset
coor_system	The coordinate system that will be applied to the input. Valid values are a `SpatialReference` object, a file with a `.prj` extension, or a string representation of a coordinate system.	Coordinate System

in_dataset

The dataset or feature class whose projection will be defined.

Feature Layer; Geodataset

coor_system

The coordinate system that will be applied to the input.

Valid values are a SpatialReference object, a file with a .prj extension, or a string representation of a coordinate system.

Coordinate System

Derived output

Name	Explanation	Data type
out_dataset	The updated input geodataset.	Geodataset

Code sample

DefineProjection example 1 (Python window)

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

import arcpy
infc = r"C:\data\citylim_unk.shp"
sr = arcpy.SpatialReference("NAD 1983 UTM Zone 11N")
arcpy.management.DefineProjection(infc, sr)

DefineProjection example 2 (stand-alone script)

The following stand-alone script uses the DefineProjection function to record coordinate system information for the input dataset.

# Name: DefineProjection.py
# Description: Records the coordinate system information for the specified input dataset or feature class

# import system modules
import arcpy

# set workspace environment
arcpy.env.workspace = "C:/data"

try:
    # set local variables
    in_dataset = "citylim_unk.shp" #"forest.shp"

    # get the coordinate system by describing a feature class
    dsc = arcpy.Describe("citylim_utm11.shp")
    coord_sys = dsc.spatialReference

    # run the tool
    arcpy.management.DefineProjection(in_dataset, coord_sys)

    # print messages when the tool runs successfully
    print(arcpy.GetMessages(0))

except arcpy.ExecuteError:
    print(arcpy.GetMessages(2))

except Exception as ex:
    print(ex.args[0])

Environments

Current Workspace, Scratch Workspace

Licensing information

Basic: Yes
Standard: Yes
Advanced: Yes

Define Projection (Data Management Tools)

Summary

Usage

Parameters

Derived output

Environments

Licensing information

Related topics