TheDefine Projectiontool is specifically used when a dataset lacks spatial reference metadata—that is, when its coordinate system is labeled as “Unknown.” This situation arises when the coordinate system information is missing or was never assigned, and it is necessary to tell ArcGIS what spatial reference the data is already in without altering the data’s location or pixel values.
According to ArcGIS Pro documentation and workflow best practices:
"The Define Projection tool assigns a coordinate system to a dataset that does not already have one. It does not alter the dataset’s data or coordinate values—only the metadata is updated."
This is crucial becauseProjectandProject Rasterare tools thattransformdata from one coordinate system to another, and they require that the data already has a valid defined coordinate system to begin with. Attempting to use either of those tools on data with an unknown projection would be incorrect and could lead to spatial inaccuracies.
Therefore, thecorrect and verified toolfor this situation isDefine Projection.
Reference Topics Covered:
• ArcGIS Pro – Data Management → Defining spatial reference
• ArcGIS Pro – Raster Functions and Georeferencing Workflows
• ArcGIS Pro – Geoprocessing Tool Help (Define Projection vs Project Raster)
• ArcGIS Pro Certification Study Guide – Data Management Domain
