Arcpy Script tool to assign projection across all maps within a project

MadelineP — Tue, 17 Feb 2026 03:54:21 GMT

Hi everyone. I am attempting to create a script tool that assigns a coordinate system across all maps within a Pro project. The purpose of this is to avoid having to assign each projection manually after creating a new map.

I first wrote out the code with hard-coded variables, which runs perfectly:

import arcpy

# Reference the current project
aprx = arcpy.mp.ArcGISProject("CURRENT")

# Define the target coordinate system (use a WKID or Name)
# Example: 4326 is WGS 1984
new_sr = arcpy.SpatialReference(2285)

# Loop through all maps in the project
for map_obj in aprx.listMaps():
# Assign the new spatial reference to the map
map_obj.spatialReference = new_sr
print(f"Updated projection for map: {map_obj.name}")

# Save the project to commit changes
aprx.save()

This is the altered code I created to insert inside the Script tool:

import arcpy
arcpy.env.overwriteOutput = True

try:
aprx = arcpy.mp.ArcGISProject("CURRENT")

# Get the SpatialReference object directly from the tool parameter
spatial_ref = arcpy.GetParameter(0)

# Iterate through maps
for map_object in aprx.listMaps():
map_object.spatialReference = spatial_ref
arcpy.AddMessage(f"Updated projection for: {map_object.name}")

# Save once after all updates are complete
aprx.save()
arcpy.AddMessage("All maps updated and project saved.")

except Exception as e:
arcpy.AddError(f"Error assigning coordinate systems: {str(e)}")

When I run the script, I am prompted to select a coordinate system, which is exactly what I want. However, when I run the script, it fails with the error message Error assigning coordinate systems: SpatialReference: Input value is not valid.

These are my parameters within the script.

I know that it's something related to the coordinate system input parameter, I just can't figure out what. FYI I am a beginner to coding/making script tools so please give me advice in layman's terms 🙂 TIA!!

Re: Arcpy Script tool to assign projection across all maps within a project

DanPatterson — Tue, 17 Feb 2026 11:01:47 GMT

There is a "Spatial Reference" under the Data Type drop down... did you try it

Re: Arcpy Script tool to assign projection across all maps within a project

MadelineP — Tue, 17 Feb 2026 17:11:14 GMT

Hi, that worked! I knew it was an easy fix, thanks for pointing me in the right direction 🙂

topic Re: Arcpy Script tool to assign projection across all maps within a project in ArcGIS Pro Questions

Arcpy Script tool to assign projection across all maps within a project

Re: Arcpy Script tool to assign projection across all maps within a project

Re: Arcpy Script tool to assign projection across all maps within a project