What is the primary purpose of the Define Projection tool in ArcGIS Pro?

The primary purpose of the Define Projection tool in ArcGIS Pro is to assign missing projection information to a dataset. When working with geographic data, it is essential for that data to have associated information about its coordinate system, or projection. This tool is particularly useful when a dataset is lacking metadata that specifies how the data should be interpreted spatially. By using the Define Projection tool, users can properly assign the correct projection to datasets that do not have this information, which allows for accurate representation and analysis within the GIS environment.

For instance, if a shapefile or any other geographic dataset is created without proper projection details, it might not display correctly on the map, leading to confusion and errors in analysis. By defining the projection, GIS users ensure that their data aligns correctly with other spatial data, facilitating better integration and analysis.

In the other options, changing the coordinate system of a layer involves reprojecting data, which is not the same as simply defining its projection. Creating a new map layout pertains to the arrangement and design of the map for presentation purposes, and enhancing data visualization involves techniques to improve how the data is visually represented, rather than assigning fundamental projection information.